Not related to the above, but also noticed that the carrierService is being called before the shipping part.
Instead of being called when on the shipping part of the Checkout, it is being called on the the information part?
This might be the reason why the rates we are passing through the API isn't showing on the shipping part.
Does anyone also experience this?? I am sure the API call was called just on check out and not on shipping part, it logged the post on our database.
I don't believe the request payload that Shopify sends to the CarrierService can be customized from what is listed here.
Regarding your other question, it's possible that Shopify prefetches before proceeding to checkout to improve the user experience, in the case where the external CarrierService may fail to respond by the time the customer reaches checkout.
Thank you for answering the first question.
For the second one... if the shopify prefetches, won't the values be null, because the user hasn't input any information yet? have been logging the values being posted by shopify but the destination is always null. Also have hardcoded a simple return yet it is still not showing, have tried using postman and it's getting a result there.
see screenshot below