Tax Partner apps can now receive cart line properties in tax calculation requests

As of API version 2026-04, tax calculation requests for Tax Partner Apps can now include cart line item properties. These properties are custom name-value pairs that merchants can add to individual line items.

• Merchants configure properties on individual cart line items (such as token, personalization, or gift_wrap).
• Tax Partner Apps specify which property keys they want to receive across all line items
• Only the requested property keys are included in calculation requests.

Key limits

You can specify a maximum of five keys. The five key limit applies to which property keys the Partner wants to receive, not the number of line items. For example:

• Partner configures: ["token", "personalization"] (2 keys)
• Cart has: 10 line items
• Result: All 10 line items will include their own token and personalization values (if present)

Example payload

Cart line items in the delivery_groups[].cart_lines[] objects now include an optional properties field per line item.

Before (2026-04):

{
  "delivery_groups": [{
    "cart_lines": [{
      "id": "gid://shopify/CartLine/123",
      "quantity": 1,
      "merchandise": {
        "id": "gid://shopify/ProductVariant/456",
        "title": "Custom T-Shirt"
      },
      "cost": {
        "amount_per_quantity": {
          "currency_code": "USD",
          "amount": "25.00"
        }
      }
    }]
  }]
}

(2026-04) & After:

{
  "delivery_groups": [{
    "cart_lines": [
      {
        "id": "gid://shopify/CartLine/7",
        "quantity": 1,
        "merchandise": {
          "id": "gid://shopify/ProductVariant/456",
          "title": "Custom T-Shirt"
        },
        "cost": {
          "amount_per_quantity": {
            "currency_code": "USD",
            "amount": "25.00"
          }
        },
        "properties": {
          "token": "abc-123",
          "personalization": "John Smith"
        }
      },
      {
        "id": "gid://shopify/CartLine/6",
        "quantity": 2,
        "merchandise": {
          "id": "gid://shopify/ProductVariant/789",
          "title": "Custom Mug"
        },
        "cost": {
          "amount_per_quantity": {
            "currency_code": "USD",
            "amount": "15.00"
          }
        },
        "properties": {
          "token": "def-456",
          "personalization": "Jane Doe"
        }
      }
    ]
  }]
}