My team is running into the following issue with express checkout:
We have an app with a cart validation functions that checks, based on an HMAC key that we set in the cart via an App block, whether a customer is allowed to add a product to their cart.
With express checkout, when a customer clicks the Buy with Shop Pay button on the product page we can see that a completely new cart gets created, with the product already in it. This causes in turn for our validation function to fail because there is no chance for the valdiation function to be added to the new cart.
Is there any way we can implement our validation approach with Express checkout buttons like the checkout with shop pay button on the product page?