Tax Partner Apps Can Now Receive Cart Line Properties in Tax Calculation Requests

Overview

As of API version 2026-01, 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.

What's New

Tax Partner Apps can now receive line item properties in tax calculation requests by configuring which property keys they want to receive.

Property Configuration

• Merchants configure properties on individual cart line items (e.g., "token", "personalization", "gift_wrap")
• Tax Partner Apps specify which property keys they want to receive across all line items (maximum 5 keys)
• Only the requested property keys are included in calculation requests

How It Works: Per-Line-Item Properties

The 5-key limit applies to which property keys the partner wants to receive, not the number of line items:

• 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)

Request Payload Changes

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

Before (2026-01):

{
  "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"
        }
      }
    }]
  }]
}

After (2026-01):

{
  "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"
        }
      }
    ]
  }]
}