How to pass a discount code to cartCreate mutation when using "Buy It Now" button?

[Nmh11]

Short description of issue

cartCreate Mutation Ignoring Hidden Discount Input

Reproduction steps

input type=“hidden” name=“discount” value=“AXVNX”>

click “buy Now”

Additional info

I’m trying to implement a feature where a discount code is automatically applied when a customer clicks the “Buy It Now” button on the Product Detail Page.

My current approach: I added a hidden input field named discount inside the product form: ‘input type=“hidden” name=“discount” value=“AXVNX”>’

The issue: When clicking “Buy It Now”, the browser executes a cartCreate mutation to api/unstable/graphql.json. However, looking at the Network tab in DevTools, the discountCodes array in the payload remains empty: discountCodes: .

It seems the default Shopify scripts for the “Buy It Now” button (which usually triggers a dynamic checkout) do not pick up additional input fields from the form liquid to include them in the GraphQL mutation.

What I want to achieve: I need the discountCodes variable in the cartCreate mutation to be populated with my value (e.g., [“AXVNX”]) so the discount is applied immediately on the checkout page.

What type of topic is this

Troubleshooting

Upload screenshot(s) of issue

[Paige-Shopify]

Only the update endpoint of the Cart AJAX API supports adding discounts. When you add a product to the cart it uses the add endpoint. This is why your hidden input doesn’t work.

The dynamic checkout button changes based on a shop’s settings and individual customer’s preferences. When customers see “Buy It Now” instead of an external payment method, you can still apply discounts by using a Checkout UI Extension app.