v1.81.0 (February 6, 2026)

const session = await client.checkoutSessions.create({
  product_cart: [{ product_id: 'pdt_123', quantity: 1 }],
  customization: {
    theme_config: {
      radius: '8px',
      pay_button_text: 'Complete Purchase',
      light: { button_primary: '#0066ff', text_primary: '#1a1a1a' },
      dark: { button_primary: '#3385ff', text_primary: '#ffffff' }
    }
  },
  return_url: 'https://yoursite.com/return'
});

await client.subscriptions.changePlan('sub_123', {
  product_id: 'pdt_pro',
  quantity: 1,
  proration_billing_mode: 'prorated_immediately',
  on_payment_failure: 'prevent_change'
});