> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dodopayments.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Upsells & Downsells

> Increase revenue with one-click purchases using saved payment methods for post-purchase offers, subscription upgrades, and cross-sells.

<Info>
  追加销售和降级销售允许您使用客户已保存的支付方式提供附加产品或计划更改。这使得可以实现跳过支付收集的一键购买，从而显著提高转化率。
</Info>

<CardGroup cols={3}>
  <Card title="Post-Purchase Upsells" icon="cart-plus">
    使用一键购买在结账后立即提供互补产品。
  </Card>

  <Card title="Subscription Upgrades" icon="arrow-up">
    利用自动比例分配和即时结算将客户迁移到更高层级。
  </Card>

  <Card title="Cross-Sells" icon="grid-2-plus">
    向现有客户添加相关产品，无需重新输入支付信息。
  </Card>
</CardGroup>

## 概述

追加销售和降级销售是强大的营收优化策略：

* **追加销售**：提供更高价值的产品或升级（例如将基本计划升级到专业计划）
* **降级销售**：当客户拒绝或降级时提供低价替代选项
* **交叉销售**：建议互补产品（例如附加组件、相关商品）

Dodo Payments 通过 `payment_method_id` 参数启用这些流程，该参数使您可以在无需客户重新输入卡片详细信息的情况下收取其已保存的支付方式。

### 主要收益

| 收益         | 影响                        |
| ---------- | ------------------------- |
| **一键购买**   | 完全跳过返回客户的支付表单             |
| **更高转化率**  | 在决策时刻减少摩擦                 |
| **即时处理**   | 使用 `confirm: true` 立即处理费用 |
| **无缝用户体验** | 客户在整个流程中始终留在您的应用内         |

## 工作原理

```mermaid theme={null}
sequenceDiagram
    participant C as Customer
    participant A as Your App
    participant D as Dodo API
    
    C->>A: Completes purchase
    A->>D: Get payment methods
    D-->>A: payment_method_id
    A->>C: Show upsell offer
    C->>A: Accept (one click)
    A->>D: Charge with payment_method_id
    D-->>A: Payment success
    D->>A: Webhook: payment.succeeded
```

## 前提条件

在实施追加销售和降级销售之前，请确保您已完成以下准备工作：

<Steps>
  <Step title="Customer with Saved Payment Method">
    客户必须至少完成一次购买。客户完成结账后，支付方式会自动保存。
  </Step>

  <Step title="Products Configured">
    在 Dodo Payments 仪表板中创建您的追加销售产品。这些可以是一次性付款、订阅或附加组件。
  </Step>

  <Step title="Webhook Endpoint">
    设置 Webhook 以处理 `payment.succeeded`、`payment.failed` 和 `subscription.plan_changed` 事件。
  </Step>
</Steps>

## 获取客户支付方式

在提供追加销售之前，请检索客户已保存的支付方式：

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    import DodoPayments from 'dodopayments';

    const client = new DodoPayments({
      bearerToken: process.env.DODO_PAYMENTS_API_KEY,
      environment: 'live_mode',
    });

    async function getPaymentMethods(customerId: string) {
      const paymentMethods = await client.customers.retrievePaymentMethods(customerId);
      
      // Returns array of saved payment methods
      // Each has: payment_method_id, type, card (last4, brand, exp_month, exp_year)
      return paymentMethods;
    }

    // Example usage
    const methods = await getPaymentMethods('cus_123');
    console.log('Available payment methods:', methods);

    // Use the first available method for upsell
    const primaryMethod = methods[0]?.payment_method_id;
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    import os
    from dodopayments import DodoPayments

    client = DodoPayments(
        bearer_token=os.environ.get("DODO_PAYMENTS_API_KEY"),
        environment="live_mode",
    )

    def get_payment_methods(customer_id: str):
        payment_methods = client.customers.retrieve_payment_methods(customer_id)
        
        # Returns list of saved payment methods
        # Each has: payment_method_id, type, card (last4, brand, exp_month, exp_year)
        return payment_methods

    # Example usage
    methods = get_payment_methods("cus_123")
    print("Available payment methods:", methods)

    # Use the first available method for upsell
    primary_method = methods[0].payment_method_id if methods else None
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    package main

    import (
        "context"
        "fmt"
        "github.com/dodopayments/dodopayments-go"
        "github.com/dodopayments/dodopayments-go/option"
    )

    func getPaymentMethods(customerID string) ([]dodopayments.CustomerGetPaymentMethodsResponseItem, error) {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        resp, err := client.Customers.GetPaymentMethods(
            context.TODO(),
            customerID,
        )
        if err != nil {
            return nil, err
        }
        
        return resp.Items, nil
    }

    func main() {
        methods, err := getPaymentMethods("cus_123")
        if err != nil {
            panic(err)
        }
        
        fmt.Println("Available payment methods:", methods)
        
        // Use the first available method for upsell
        if len(methods) > 0 {
            primaryMethod := methods[0].PaymentMethodID
            fmt.Println("Primary method:", primaryMethod)
        }
    }
    ```
  </Tab>
</Tabs>

<Info>
  支付方式在客户完成结账后会自动保存。您无需手动保存。
</Info>

## 购后的一键追加销售

在成功购买后立即提供附加产品。客户可以一键接受，因为他们的支付方式已保存。

```mermaid theme={null}
flowchart LR
    A[Purchase] --> B{Upsell?}
    B -->|Yes| C[Show Offer]
    B -->|No| F[Done]
    C --> D{Accept?}
    D -->|Yes| E[One-Click Charge] --> F
    D -->|No| F
```

### 实施

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    import DodoPayments from 'dodopayments';

    const client = new DodoPayments({
      bearerToken: process.env.DODO_PAYMENTS_API_KEY,
      environment: 'live_mode',
    });

    async function createOneClickUpsell(
      customerId: string,
      paymentMethodId: string,
      upsellProductId: string
    ) {
      // Create checkout session with saved payment method
      // confirm: true processes the payment immediately
      const session = await client.checkoutSessions.create({
        product_cart: [
          {
            product_id: upsellProductId,
            quantity: 1
          }
        ],
        customer: {
          customer_id: customerId
        },
        payment_method_id: paymentMethodId,
        confirm: true,  // Required when using payment_method_id
        return_url: 'https://yourapp.com/upsell-success',
        feature_flags: {
          redirect_immediately: true  // Skip success page
        },
        metadata: {
          upsell_source: 'post_purchase',
          original_order_id: 'order_123'
        }
      });

      return session;
    }

    // Example: Offer premium add-on after initial purchase
    async function handlePostPurchaseUpsell(customerId: string) {
      // Get customer's payment methods
      const methods = await client.customers.retrievePaymentMethods(customerId);
      
      if (methods.length === 0) {
        console.log('No saved payment methods available');
        return null;
      }

      // Create the upsell with one-click checkout
      const upsell = await createOneClickUpsell(
        customerId,
        methods[0].payment_method_id,
        'prod_premium_addon'
      );

      console.log('Upsell processed:', upsell.session_id);
      return upsell;
    }
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    import os
    from dodopayments import DodoPayments

    client = DodoPayments(
        bearer_token=os.environ.get("DODO_PAYMENTS_API_KEY"),
        environment="live_mode",
    )

    def create_one_click_upsell(
        customer_id: str,
        payment_method_id: str,
        upsell_product_id: str
    ):
        """Create a one-click upsell using saved payment method."""
        
        # Create checkout session with saved payment method
        # confirm=True processes the payment immediately
        session = client.checkout_sessions.create(
            product_cart=[
                {
                    "product_id": upsell_product_id,
                    "quantity": 1
                }
            ],
            customer={
                "customer_id": customer_id
            },
            payment_method_id=payment_method_id,
            confirm=True,  # Required when using payment_method_id
            return_url="https://yourapp.com/upsell-success",
            feature_flags={
                "redirect_immediately": True  # Skip success page
            },
            metadata={
                "upsell_source": "post_purchase",
                "original_order_id": "order_123"
            }
        )
        
        return session

    def handle_post_purchase_upsell(customer_id: str):
        """Offer premium add-on after initial purchase."""
        
        # Get customer's payment methods
        methods = client.customers.retrieve_payment_methods(customer_id)
        
        if not methods:
            print("No saved payment methods available")
            return None
        
        # Create the upsell with one-click checkout
        upsell = create_one_click_upsell(
            customer_id=customer_id,
            payment_method_id=methods[0].payment_method_id,
            upsell_product_id="prod_premium_addon"
        )
        
        print(f"Upsell processed: {upsell.session_id}")
        return upsell
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    package main

    import (
        "context"
        "fmt"
        "os"
        
        "github.com/dodopayments/dodopayments-go"
        "github.com/dodopayments/dodopayments-go/option"
    )

    func createOneClickUpsell(
        customerID string,
        paymentMethodID string,
        upsellProductID string,
    ) (*dodopayments.CheckoutSessionResponse, error) {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        // Create checkout session with saved payment method
        // Confirm: true processes the payment immediately
        session, err := client.CheckoutSessions.New(context.TODO(), dodopayments.CheckoutSessionNewParams{
            CheckoutSessionRequest: dodopayments.CheckoutSessionRequestParam{
                ProductCart: dodopayments.F([]dodopayments.ProductItemReqParam{
                    {
                        ProductID: dodopayments.F(upsellProductID),
                        Quantity:  dodopayments.F(int64(1)),
                    },
                }),
                Customer: dodopayments.F[dodopayments.CustomerRequestUnionParam](
                    dodopayments.AttachExistingCustomerParam{
                        CustomerID: dodopayments.F(customerID),
                    },
                ),
                PaymentMethodID: dodopayments.F(paymentMethodID),
                Confirm:         dodopayments.F(true), // Required when using payment_method_id
                ReturnURL:       dodopayments.F("https://yourapp.com/upsell-success"),
                FeatureFlags: dodopayments.F(dodopayments.CheckoutSessionFlagsParam{
                    RedirectImmediately: dodopayments.F(true), // Skip success page
                }),
                Metadata: dodopayments.F(map[string]string{
                    "upsell_source":     "post_purchase",
                    "original_order_id": "order_123",
                }),
            },
        })
        
        return session, err
    }

    func handlePostPurchaseUpsell(customerID string) (*dodopayments.CheckoutSessionResponse, error) {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        // Get customer's payment methods
        resp, err := client.Customers.GetPaymentMethods(context.TODO(), customerID)
        if err != nil {
            return nil, err
        }
        
        if len(resp.Items) == 0 {
            fmt.Println("No saved payment methods available")
            return nil, nil
        }
        
        // Create the upsell with one-click checkout
        upsell, err := createOneClickUpsell(
            customerID,
            resp.Items[0].PaymentMethodID,
            "prod_premium_addon",
        )
        if err != nil {
            return nil, err
        }
        
        fmt.Printf("Upsell processed: %s\n", upsell.SessionID)
        return upsell, nil
    }
    ```
  </Tab>
</Tabs>

<Warning>
  使用 `payment_method_id` 时，您必须设置 `confirm: true` 并提供现有的 `customer_id`。支付方式必须属于该客户。
</Warning>

## 订阅升级

通过自动比例分配处理，将客户迁移到更高层级的订阅计划。

```mermaid theme={null}
sequenceDiagram
    participant C as Customer
    participant A as Your App
    participant D as Dodo API
    
    C->>A: Request upgrade
    A->>D: Preview change plan
    D-->>A: Charge amount
    A->>C: Confirm $50 charge?
    C->>A: Confirm
    A->>D: Change plan
    D->>A: Webhook: plan_changed
```

### 承诺前预览

始终预览计划更改，让客户明确知道将被收取的费用：

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    async function previewUpgrade(
      subscriptionId: string,
      newProductId: string
    ) {
      const preview = await client.subscriptions.previewChangePlan(subscriptionId, {
        product_id: newProductId,
        quantity: 1,
        proration_billing_mode: 'difference_immediately'
      });

      return {
        immediateCharge: preview.immediate_charge?.summary,
        newPlan: preview.new_plan,
        effectiveDate: preview.effective_date
      };
    }

    // Show customer the charge before confirming
    const preview = await previewUpgrade('sub_123', 'prod_pro_plan');
    console.log(`Upgrade will charge: ${preview.immediateCharge}`);
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    def preview_upgrade(subscription_id: str, new_product_id: str):
        preview = client.subscriptions.preview_change_plan(
            subscription_id=subscription_id,
            product_id=new_product_id,
            quantity=1,
            proration_billing_mode="difference_immediately"
        )
        
        return {
            "immediate_charge": preview.immediate_charge.summary if preview.immediate_charge else None,
            "new_plan": preview.new_plan,
            "effective_date": preview.effective_date
        }

    # Show customer the charge before confirming
    preview = preview_upgrade("sub_123", "prod_pro_plan")
    print(f"Upgrade will charge: {preview['immediate_charge']}")
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    func previewUpgrade(subscriptionID string, newProductID string) (map[string]interface{}, error) {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        preview, err := client.Subscriptions.PreviewChangePlan(
            context.TODO(),
            subscriptionID,
            dodopayments.SubscriptionPreviewChangePlanParams{
                UpdateSubscriptionPlanReq: dodopayments.UpdateSubscriptionPlanReqParam{
                    ProductID:            dodopayments.F(newProductID),
                    Quantity:             dodopayments.F(int64(1)),
                    ProrationBillingMode: dodopayments.F(dodopayments.UpdateSubscriptionPlanReqProrationBillingModeDifferenceImmediately),
                },
            },
        )
        if err != nil {
            return nil, err
        }
        
        return map[string]interface{}{
            "immediate_charge": preview.ImmediateCharge.Summary,
            "new_plan":         preview.NewPlan,
            "effective_at":     preview.ImmediateCharge.EffectiveAt,
        }, nil
    }
    ```
  </Tab>
</Tabs>

### 执行升级

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    async function upgradeSubscription(
      subscriptionId: string,
      newProductId: string,
      prorationMode: 'prorated_immediately' | 'difference_immediately' | 'full_immediately' = 'difference_immediately'
    ) {
      const result = await client.subscriptions.changePlan(subscriptionId, {
        product_id: newProductId,
        quantity: 1,
        proration_billing_mode: prorationMode
      });

      return {
        status: result.status,
        subscriptionId: result.subscription_id,
        paymentId: result.payment_id,
        invoiceId: result.invoice_id
      };
    }

    // Upgrade from Basic ($30) to Pro ($80)
    // With difference_immediately: charges $50 instantly
    const upgrade = await upgradeSubscription('sub_123', 'prod_pro_plan');
    console.log('Upgrade status:', upgrade.status);
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    def upgrade_subscription(
        subscription_id: str,
        new_product_id: str,
        proration_mode: str = "difference_immediately"
    ):
        result = client.subscriptions.change_plan(
            subscription_id=subscription_id,
            product_id=new_product_id,
            quantity=1,
            proration_billing_mode=proration_mode
        )
        
        return {
            "status": result.status,
            "subscription_id": result.subscription_id,
            "payment_id": result.payment_id,
            "invoice_id": result.invoice_id
        }

    # Upgrade from Basic ($30) to Pro ($80)
    # With difference_immediately: charges $50 instantly
    upgrade = upgrade_subscription("sub_123", "prod_pro_plan")
    print(f"Upgrade status: {upgrade['status']}")
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    func upgradeSubscription(
        subscriptionID string,
        newProductID string,
        prorationMode dodopayments.UpdateSubscriptionPlanReqProrationBillingMode,
    ) error {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        // ChangePlan returns no response body; a nil error means the change succeeded.
        err := client.Subscriptions.ChangePlan(
            context.TODO(),
            subscriptionID,
            dodopayments.SubscriptionChangePlanParams{
                UpdateSubscriptionPlanReq: dodopayments.UpdateSubscriptionPlanReqParam{
                    ProductID:            dodopayments.F(newProductID),
                    Quantity:             dodopayments.F(int64(1)),
                    ProrationBillingMode: dodopayments.F(prorationMode),
                },
            },
        )
        
        return err
    }

    // Upgrade from Basic ($30) to Pro ($80)
    // With DifferenceImmediately: charges $50 instantly
    err := upgradeSubscription(
        "sub_123",
        "prod_pro_plan",
        dodopayments.UpdateSubscriptionPlanReqProrationBillingModeDifferenceImmediately,
    )
    if err != nil {
        panic(err)
    }
    fmt.Println("Upgrade succeeded")
    ```
  </Tab>
</Tabs>

### 比例分配模式

选择升级时如何向客户收费：

| 模式                       | 行为                      | 适用场景      |
| ------------------------ | ----------------------- | --------- |
| `difference_immediately` | 即时收取价格差（$30→$80 = \$50） | 简单升级      |
| `prorated_immediately`   | 按结算周期剩余时间计费             | 公平的基于时间计费 |
| `full_immediately`       | 收取全新的计划价格，忽略剩余时间        | 重置计费周期    |

<Tip>
  对于直接的升级流程，请使用 `difference_immediately`。若想考虑当前计划尚未使用的时间，请使用 `prorated_immediately`。
</Tip>

## 交叉销售

向现有客户添加互补产品，无需重新输入支付信息。

```mermaid theme={null}
flowchart LR
    A[View Product] --> B{Existing Customer?}
    B -->|Yes| C[One-Click Buy] --> E[Deliver]
    B -->|No| D[Standard Checkout] --> E
```

### 实施

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    async function createCrossSell(
      customerId: string,
      paymentMethodId: string,
      productId: string,
      quantity: number = 1
    ) {
      // Create a one-time payment using saved payment method
      const payment = await client.payments.create({
        product_cart: [
          {
            product_id: productId,
            quantity: quantity
          }
        ],
        customer_id: customerId,
        payment_method_id: paymentMethodId,
        return_url: 'https://yourapp.com/purchase-complete',
        metadata: {
          purchase_type: 'cross_sell',
          source: 'product_recommendation'
        }
      });

      return payment;
    }

    // Example: Customer bought a course, offer related ebook
    async function offerRelatedProduct(customerId: string, relatedProductId: string) {
      const methods = await client.customers.retrievePaymentMethods(customerId);
      
      if (methods.length === 0) {
        // Fall back to standard checkout
        return client.checkoutSessions.create({
          product_cart: [{ product_id: relatedProductId, quantity: 1 }],
          customer: { customer_id: customerId },
          return_url: 'https://yourapp.com/purchase-complete'
        });
      }

      // One-click purchase
      return createCrossSell(customerId, methods[0].payment_method_id, relatedProductId);
    }
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    def create_cross_sell(
        customer_id: str,
        payment_method_id: str,
        product_id: str,
        quantity: int = 1
    ):
        """Create a one-time payment using saved payment method."""
        
        payment = client.payments.create(
            product_cart=[
                {
                    "product_id": product_id,
                    "quantity": quantity
                }
            ],
            customer_id=customer_id,
            payment_method_id=payment_method_id,
            return_url="https://yourapp.com/purchase-complete",
            metadata={
                "purchase_type": "cross_sell",
                "source": "product_recommendation"
            }
        )
        
        return payment

    def offer_related_product(customer_id: str, related_product_id: str):
        """Offer related product with one-click purchase if possible."""
        
        methods = client.customers.retrieve_payment_methods(customer_id)
        
        if not methods:
            # Fall back to standard checkout
            return client.checkout_sessions.create(
                product_cart=[{"product_id": related_product_id, "quantity": 1}],
                customer={"customer_id": customer_id},
                return_url="https://yourapp.com/purchase-complete"
            )
        
        # One-click purchase
        return create_cross_sell(customer_id, methods[0].payment_method_id, related_product_id)
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    func createCrossSell(
        customerID string,
        paymentMethodID string,
        productID string,
        quantity int64,
    ) (*dodopayments.PaymentNewResponse, error) {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        payment, err := client.Payments.New(context.TODO(), dodopayments.PaymentNewParams{
            ProductCart: dodopayments.F([]dodopayments.OneTimeProductCartItemParam{
                {
                    ProductID: dodopayments.F(productID),
                    Quantity:  dodopayments.F(quantity),
                },
            }),
            Customer: dodopayments.F[dodopayments.CustomerRequestUnionParam](
                dodopayments.AttachExistingCustomerParam{CustomerID: dodopayments.F(customerID)},
            ),
            Billing: dodopayments.F(dodopayments.BillingAddressParam{
                Country: dodopayments.F(dodopayments.CountryCodeUs),
                City:    dodopayments.F("San Francisco"),
                State:   dodopayments.F("CA"),
                Street:  dodopayments.F("1 Market St"),
                Zipcode: dodopayments.F("94105"),
            }),
            PaymentMethodID: dodopayments.F(paymentMethodID),
            ReturnURL:       dodopayments.F("https://yourapp.com/purchase-complete"),
            Metadata: dodopayments.F(map[string]string{
                "purchase_type": "cross_sell",
                "source":        "product_recommendation",
            }),
        })
        
        return payment, err
    }

    func offerRelatedProduct(customerID string, relatedProductID string) (interface{}, error) {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        resp, err := client.Customers.GetPaymentMethods(context.TODO(), customerID)
        if err != nil {
            return nil, err
        }
        
        if len(resp.Items) == 0 {
            // Fall back to standard checkout
            return client.CheckoutSessions.New(context.TODO(), dodopayments.CheckoutSessionNewParams{
                CheckoutSessionRequest: dodopayments.CheckoutSessionRequestParam{
                    ProductCart: dodopayments.F([]dodopayments.ProductItemReqParam{
                        {ProductID: dodopayments.F(relatedProductID), Quantity: dodopayments.F(int64(1))},
                    }),
                    Customer: dodopayments.F[dodopayments.CustomerRequestUnionParam](
                        dodopayments.AttachExistingCustomerParam{CustomerID: dodopayments.F(customerID)},
                    ),
                    ReturnURL: dodopayments.F("https://yourapp.com/purchase-complete"),
                },
            })
        }
        
        // One-click purchase
        return createCrossSell(customerID, resp.Items[0].PaymentMethodID, relatedProductID, 1)
    }
    ```
  </Tab>
</Tabs>

## 订阅降级

当客户希望转到更低层级计划时，请通过自动抵扣优雅处理过渡。

### 降级如何运作

1. 客户申请降级（专业版 → 基础版）
2. 系统计算当前计划剩余价值
3. 将信用额度添加到订阅以用于未来续订
4. 客户立即迁移到新计划

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    async function downgradeSubscription(
      subscriptionId: string,
      newProductId: string
    ) {
      // Preview the downgrade first
      const preview = await client.subscriptions.previewChangePlan(subscriptionId, {
        product_id: newProductId,
        quantity: 1,
        proration_billing_mode: 'difference_immediately'
      });

      console.log('Credit to be applied:', preview.credit_amount);

      // Execute the downgrade
      const result = await client.subscriptions.changePlan(subscriptionId, {
        product_id: newProductId,
        quantity: 1,
        proration_billing_mode: 'difference_immediately'
      });

      // Credits are automatically applied to future renewals
      return result;
    }

    // Downgrade from Pro ($80) to Basic ($30)
    // $50 credit added to subscription, auto-applied on next renewal
    const downgrade = await downgradeSubscription('sub_123', 'prod_basic_plan');
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    def downgrade_subscription(subscription_id: str, new_product_id: str):
        # Preview the downgrade first
        preview = client.subscriptions.preview_change_plan(
            subscription_id=subscription_id,
            product_id=new_product_id,
            quantity=1,
            proration_billing_mode="difference_immediately"
        )
        
        print(f"Credit to be applied: {preview.credit_amount}")
        
        # Execute the downgrade
        result = client.subscriptions.change_plan(
            subscription_id=subscription_id,
            product_id=new_product_id,
            quantity=1,
            proration_billing_mode="difference_immediately"
        )
        
        # Credits are automatically applied to future renewals
        return result

    # Downgrade from Pro ($80) to Basic ($30)
    # $50 credit added to subscription, auto-applied on next renewal
    downgrade = downgrade_subscription("sub_123", "prod_basic_plan")
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    func downgradeSubscription(subscriptionID string, newProductID string) error {
        client := dodopayments.NewClient(
            option.WithBearerToken(os.Getenv("DODO_PAYMENTS_API_KEY")),
        )
        
        // Preview the downgrade first
        preview, err := client.Subscriptions.PreviewChangePlan(
            context.TODO(),
            subscriptionID,
            dodopayments.SubscriptionPreviewChangePlanParams{
                UpdateSubscriptionPlanReq: dodopayments.UpdateSubscriptionPlanReqParam{
                    ProductID:            dodopayments.F(newProductID),
                    Quantity:             dodopayments.F(int64(1)),
                    ProrationBillingMode: dodopayments.F(dodopayments.UpdateSubscriptionPlanReqProrationBillingModeDifferenceImmediately),
                },
            },
        )
        if err != nil {
            return err
        }
        
        fmt.Printf("Customer credits to be applied: %v\n", preview.ImmediateCharge.Summary.CustomerCredits)
        
        // Execute the downgrade (returns no response body; nil error means success)
        return client.Subscriptions.ChangePlan(
            context.TODO(),
            subscriptionID,
            dodopayments.SubscriptionChangePlanParams{
                UpdateSubscriptionPlanReq: dodopayments.UpdateSubscriptionPlanReqParam{
                    ProductID:            dodopayments.F(newProductID),
                    Quantity:             dodopayments.F(int64(1)),
                    ProrationBillingMode: dodopayments.F(dodopayments.UpdateSubscriptionPlanReqProrationBillingModeDifferenceImmediately),
                },
            },
        )
    }
    ```
  </Tab>
</Tabs>

<Info>
  使用 `difference_immediately` 的降级所产生的信用额度是订阅范围内的，并会自动应用于未来续订。它们不同于 [Customer Credits](/features/customer-credit)。
</Info>

## 完整示例：购后追加销售流程

以下是一个完整实现，展示如何在成功购买后提供追加销售：

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    import DodoPayments from 'dodopayments';
    import express from 'express';

    const client = new DodoPayments({
      bearerToken: process.env.DODO_PAYMENTS_API_KEY,
      environment: 'live_mode',
    });

    const app = express();

    // Store for tracking upsell eligibility (use your database in production)
    const eligibleUpsells = new Map<string, { customerId: string; productId: string }>();

    // Webhook handler for initial purchase success
    app.post('/webhooks/dodo', express.raw({ type: 'application/json' }), async (req, res) => {
      const event = JSON.parse(req.body.toString());
      
      switch (event.type) {
        case 'payment.succeeded':
          // Check if customer is eligible for upsell
          const customerId = event.data.customer_id;
          const productId = event.data.product_id;
          
          // Define upsell rules (e.g., bought Basic, offer Pro)
          const upsellProduct = getUpsellProduct(productId);
          
          if (upsellProduct) {
            eligibleUpsells.set(customerId, {
              customerId,
              productId: upsellProduct
            });
          }
          break;
          
        case 'payment.failed':
          console.log('Payment failed:', event.data.payment_id);
          // Handle failed upsell payment
          break;
      }
      
      res.json({ received: true });
    });

    // API endpoint to check upsell eligibility
    app.get('/api/upsell/:customerId', async (req, res) => {
      const { customerId } = req.params;
      const upsell = eligibleUpsells.get(customerId);
      
      if (!upsell) {
        return res.json({ eligible: false });
      }
      
      // Get payment methods
      const methods = await client.customers.retrievePaymentMethods(customerId);
      
      if (methods.length === 0) {
        return res.json({ eligible: false, reason: 'no_payment_method' });
      }
      
      // Get product details for display
      const product = await client.products.retrieve(upsell.productId);
      
      res.json({
        eligible: true,
        product: {
          id: product.product_id,
          name: product.name,
          price: product.price,
          currency: product.currency
        },
        paymentMethodId: methods[0].payment_method_id
      });
    });

    // API endpoint to accept upsell
    app.post('/api/upsell/:customerId/accept', async (req, res) => {
      const { customerId } = req.params;
      const upsell = eligibleUpsells.get(customerId);
      
      if (!upsell) {
        return res.status(400).json({ error: 'No upsell available' });
      }
      
      try {
        const methods = await client.customers.retrievePaymentMethods(customerId);
        
        // Create one-click purchase
        const session = await client.checkoutSessions.create({
          product_cart: [{ product_id: upsell.productId, quantity: 1 }],
          customer: { customer_id: customerId },
          payment_method_id: methods[0].payment_method_id,
          confirm: true,
          return_url: `${process.env.APP_URL}/upsell-success`,
          feature_flags: { redirect_immediately: true },
          metadata: { upsell: 'true', source: 'post_purchase' }
        });
        
        // Clear the upsell offer
        eligibleUpsells.delete(customerId);
        
        res.json({ success: true, sessionId: session.session_id });
      } catch (error) {
        console.error('Upsell failed:', error);
        res.status(500).json({ error: 'Upsell processing failed' });
      }
    });

    // Helper function to determine upsell product
    function getUpsellProduct(purchasedProductId: string): string | null {
      const upsellMap: Record<string, string> = {
        'prod_basic_plan': 'prod_pro_plan',
        'prod_starter_course': 'prod_complete_bundle',
        'prod_single_license': 'prod_team_license'
      };
      
      return upsellMap[purchasedProductId] || null;
    }

    app.listen(3000);
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    import os
    from flask import Flask, request, jsonify
    from dodopayments import DodoPayments

    client = DodoPayments(
        bearer_token=os.environ.get("DODO_PAYMENTS_API_KEY"),
        environment="live_mode",
    )

    app = Flask(__name__)

    # Store for tracking upsell eligibility (use your database in production)
    eligible_upsells = {}

    @app.route('/webhooks/dodo', methods=['POST'])
    def webhook_handler():
        event = request.json
        
        if event['type'] == 'payment.succeeded':
            # Check if customer is eligible for upsell
            customer_id = event['data']['customer_id']
            product_id = event['data']['product_id']
            
            # Define upsell rules
            upsell_product = get_upsell_product(product_id)
            
            if upsell_product:
                eligible_upsells[customer_id] = {
                    'customer_id': customer_id,
                    'product_id': upsell_product
                }
        
        elif event['type'] == 'payment.failed':
            print(f"Payment failed: {event['data']['payment_id']}")
        
        return jsonify({'received': True})

    @app.route('/api/upsell/<customer_id>', methods=['GET'])
    def check_upsell(customer_id):
        upsell = eligible_upsells.get(customer_id)
        
        if not upsell:
            return jsonify({'eligible': False})
        
        # Get payment methods
        methods = client.customers.retrieve_payment_methods(customer_id)
        
        if not methods:
            return jsonify({'eligible': False, 'reason': 'no_payment_method'})
        
        # Get product details for display
        product = client.products.retrieve(upsell['product_id'])
        
        return jsonify({
            'eligible': True,
            'product': {
                'id': product.product_id,
                'name': product.name,
                'price': product.price,
                'currency': product.currency
            },
            'payment_method_id': methods[0].payment_method_id
        })

    @app.route('/api/upsell/<customer_id>/accept', methods=['POST'])
    def accept_upsell(customer_id):
        upsell = eligible_upsells.get(customer_id)
        
        if not upsell:
            return jsonify({'error': 'No upsell available'}), 400
        
        try:
            methods = client.customers.retrieve_payment_methods(customer_id)
            
            # Create one-click purchase
            session = client.checkout_sessions.create(
                product_cart=[{'product_id': upsell['product_id'], 'quantity': 1}],
                customer={'customer_id': customer_id},
                payment_method_id=methods[0].payment_method_id,
                confirm=True,
                return_url=f"{os.environ['APP_URL']}/upsell-success",
                feature_flags={'redirect_immediately': True},
                metadata={'upsell': 'true', 'source': 'post_purchase'}
            )
            
            # Clear the upsell offer
            del eligible_upsells[customer_id]
            
            return jsonify({'success': True, 'session_id': session.session_id})
        
        except Exception as error:
            print(f"Upsell failed: {error}")
            return jsonify({'error': 'Upsell processing failed'}), 500

    def get_upsell_product(purchased_product_id: str) -> str:
        """Determine upsell product based on purchased product."""
        upsell_map = {
            'prod_basic_plan': 'prod_pro_plan',
            'prod_starter_course': 'prod_complete_bundle',
            'prod_single_license': 'prod_team_license'
        }
        return upsell_map.get(purchased_product_id)

    if __name__ == '__main__':
        app.run(port=3000)
    ```
  </Tab>
</Tabs>

## 最佳实践

<AccordionGroup>
  <Accordion title="Time Your Upsells Strategically">
    在成功购买后立即提供追加销售是最佳时机，因为此时客户处于购买心态。其他有效时机包括：

    * 达到功能使用里程碑后
    * 接近计划额度限制时
    * 完成入职时
  </Accordion>

  <Accordion title="Validate Payment Method Eligibility">
    在尝试一键收费之前，请验证支付方式：

    * 是否与产品币种兼容
    * 是否未过期
    * 是否属于该客户

    API 会验证这些，但事先检查可提升用户体验。
  </Accordion>

  <Accordion title="Handle Failures Gracefully">
    当一键收费失败时：

    1. 回退到标准结账流程
    2. 向客户发送清晰的提示
    3. 提供更新支付方式的选项
    4. 切勿反复尝试失败的收费
  </Accordion>

  <Accordion title="Provide Clear Value Proposition">
    当客户了解价值时，追加销售的转化率更高：

    * 展示他们将获得的内容与当前计划的对比
    * 强调价格差异，而非总价
    * 利用社会认同（例如：“最受欢迎的升级”）
  </Accordion>

  <Accordion title="Respect Customer Choice">
    * 始终提供简单的拒绝方式
    * 拒绝后不要反复展示相同的追加销售
    * 跟踪并分析哪些追加销售转化，以优化提案
  </Accordion>
</AccordionGroup>

## 需要监控的 Webhook

跟踪以下 Webhook 事件，以支持追加销售和降级流程：

| 事件                          | 触发            | 操作           |
| --------------------------- | ------------- | ------------ |
| `payment.succeeded`         | 追加销售/交叉销售支付完成 | 发放产品，更新访问权限  |
| `payment.failed`            | 一键收费失败        | 显示错误，提供重试或回退 |
| `subscription.plan_changed` | 升级/降级完成       | 更新功能，发送确认    |
| `subscription.active`       | 计划变更后订阅重新激活   | 授予新层级访问权限    |

<Card title="Webhook Integration Guide" icon="webhook" href="/developer-resources/webhooks">
  了解如何设置和验证 Webhook 端点。
</Card>

## 相关资源

<CardGroup cols={2}>
  <Card title="Subscription Upgrade Guide" icon="arrows-rotate" href="/developer-resources/subscription-upgrade-downgrade">
    关于计划更改、比例分配模式以及处理失败的详细指南。
  </Card>

  <Card title="Checkout Sessions" icon="cart-shopping" href="/developer-resources/checkout-session">
    创建包含所有选项的结账会话的完整参考。
  </Card>

  <Card title="Customer Payment Methods API" icon="credit-card" href="/api-reference/customers/get-customer-payment-methods">
    列出客户支付方式的 API 参考。
  </Card>

  <Card title="Add-ons" icon="puzzle-piece" href="/features/addons">
    使用灵活附加组件增强订阅以获取更多营收。
  </Card>
</CardGroup>
