Custom IDs

To add the custom identifier to a request, use the custom_id field. The API returns the custom identifier in subsequent responses.

You can add the custom_id field at the transaction or transaction-line level:

Transaction level—The custom_id field is optional.
Transaction-line level—The custom_id field is required for schema validation, but you do not have to provide a value.

The following example shows the custom_id field in a transaction object in a request:

{
    "transaction": {
        "tax_timestamp": "2025-03-01T12:00:00Z",
        "description": "Transaction description",
        "currency_code": "EUR",
        "buyer_name": "Test buyer",
        "ship_to_address": {
            "country_code": "GB",
            "city": "Big city",
            "street_name": "Street name",
            "building_number": "100a",
            "address_detail": "2nd fl",
            "postal_code": "00000"
        },
        "billing_address": {
            "country_code": "GB",
            "city": "The big city",
            "street_name": "The street name",
            "building_number": "100a",
            "postal_code": "00000"
        },
        "transaction_lines": [
            {
                "amount": 100,
                "custom_id": "",
                "ship_from_address": {
                    "country_code": "GB"
                },
                "description": "Product 1",
                "product_class": "P",
                "product_tax_code": {
                    "class": "TPP/Goods"
                }
            },
            {
                "amount": 100,
                "custom_id": "",
                "ship_from_address": {
                    "country_code": "GB"
                },
                "description": "Shipping",
                "product_class": "S"
            }  
        ]
    }
}