We've been faced with a challenge or so it seems to integrate CarrierService for a Shopify Site. We have managed to create a carrier via the Shopify API via /admin/api/2021-01/carrier_services.json.
With all the correct details and parameters. We have also got shop locale and all necessary access at read and write level on our private app not to mention we have the right account plan. We have also made sure our callback works with a simple print_r of data that gets posted to this callback_url. However, it appears upon checkout (on the shipping page) Shopify doesn't seem to ping our callback_url to get the shipping rate info.
If anyone could be so kind to help us or point us into the right direction that would be massively appreciated.
Can you post (or DM me) a link to the shop id and carrier service id in question?
Apologies for the delay in getting back to you here. I'm pleased to confirm we've been able to resolve this issue.