I am looking to setup a process where a customer will interface with our custom app via a messaging service. The app will create a cart and add a number of line items. This is currently done using the createCart mutation on version 2021-10.
We will then forward the customer the returned 'checkout' url for them to view their cart. When the customer navigates to the checkout the cart is appears to be finalised and the customer is unable to add/remove quantities or continue shopping via the normal Shopify store to add more items. Is this use case currently unsupported, or is there a setting or another approach required to enable the checkout screen to appear as if the user had created the cart manually via the website?