v1.78.0（2026年2月2日）

const session = await client.checkoutSessions.create({
  product_cart: [{ product_id: 'prod_123', quantity: 1 }],
  custom_fields: [
    {
      key: 'company_name',
      label: 'Company Name',
      field_type: 'text',
      required: true
    },
    {
      key: 'team_size',
      label: 'Team Size',
      field_type: 'dropdown',
      options: ['1-10', '11-50', '51-200', '200+'],
      required: true
    },
    {
      key: 'newsletter',
      label: 'Subscribe to our newsletter',
      field_type: 'boolean',
      required: false
    }
  ],
  return_url: 'https://yoursite.com/success'
});

const session = await client.checkoutSessions.create({
  product_cart: [{ product_id: 'pdt_123', quantity: 1 }],
  customization: {
    force_language: 'ko' // Force Korean language
  },
  return_url: 'https://yoursite.com/success'
});