Last year, we announced the deprecation of the Checkout APIs, which Buy Button JS is dependent on. As part of this deprecation, checkout functionality will stop working on older versions of Buy Button JS on August 1, 2025 11:00 AM ET. To maintain functionality for customers to complete purchases, ensure that your app or storefront is on the latest major version of Buy Button JS (v3.0).
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/buy-button-js-must-be-upgraded-to-the-latest-version