My app will act as a both Fulfilment and Carrier Partner for Shopify stores.
I am facing a challenge where my shipping options can become invalid if checkout process takes a long time, for example due to stock becoming unavailable.
So imagine customer passes through the Shipping screen, picks a Shipping Option provided by my Carrier Service, but then postpones the payment.
Stock in my Warehouse could have become unavailable by the time order is created in Shopify, and received in my integration.
Is there any way in Shopify to enforce communication with my app before Order is created, to confirm feasibility of the Shipping Option that has been selected a while ago?
Is there a way to interrupt checkout process and come back with a custom error from my integration?
Has anyone else encountered similar problem?