POS UI extensions 2026-07 uses per-unit fixed-amount line item discounts

Starting with POS UI extensions API version 2026-07, FixedAmount line item discounts passed to setLineItemDiscount and bulkSetLineItemDiscounts from the Cart API must represent a per-unit discount.

Why it's changing

In API version 2026-04 and earlier, apps could pass a total fixed discount for the entire line item, and Shopify POS automatically converted it to a per-unit value. In API version 2026-07, this conversion no longer occurs. The value you pass is interpreted directly as the discount applied to each unit in the line item.

For example, in API version 2026-07, if you pass '5.00' on a line item with quantity 2, POS applies a $5.00 discount to each unit, for a $10.00 total discount. To apply a $5.00 total discount to a line item with quantity 2, you must instead pass '2.50' as the per-unit discount.

What you need to do

This change only affects FixedAmount line item discounts. Percentage discounts are not affected. Apps using API version 2026-04 or earlier do not need to make any changes.

Apps adopting API version 2026-07 must update their discount calculations before using the new version. If your app currently calculates discounts as a total line discount, compute the per-unit discount before calling setLineItemDiscount or bulkSetLineItemDiscounts — for example, by dividing the total discount by the line item quantity.

If the total discount does not divide evenly by the line item quantity, choose a rounded per-unit value that matches your app’s intended discount behavior and ensures the final discount is consistent with your logic.

For more information, see the Cart API reference.