How to resolve delayed checkout invalidation due to unavailable shipping options?

[spf-integrator]

Shopify Delayed Checkout Invalidation Due to Selected Shipping Not Available Anymore

Hi,

I am creating a custom 3PL integration for Shopify stores and I am facing a technical problem with how the checkout process works. My service is going to be registered as a Carrier Service to provide custom shipping options. Then, it will take a Shopify order once it's created and paid for, and provide delivery.

The problem I am facing is with delayed checkouts. My service only offers shipping options if there is stock available in the Warehouse and this is being verified before shipping options are provided.

There is a scenario where customer could have selected my Shipping option, continue to payment, and pay with a delay. The requested items can already be gone from the Warehouse by the time the order is created, which means that the selected Shipping option is not valid anymore.

Is there a way in Shopify API to:
a) re-validate if selected Shipping option is still available
b) any way for my API to be hit before the order is created so it can respond with a custom error
c) any other suggestion on how to tackle this issue?

I am aware that there is an option to cancel Shopify order and refund customer, but this journey leads to bad customer experiences. Ideally Shopify would check if the selected option is still valid - is there any way to achieve this?

Thanks!