Hi! Have you checked that you have all the permissions for the API? If not, then that can be the cause. 

For anyone having the same issue, I've solved it by fixing the base URL.  I was using the base URL ending in *.com which works fine with most endpoint, but not with fulfillments. I had to use the one ending in *.myshopify.com.  I've finally found out...

Hi,  I've been trying to create fulfillments with the admin REST API and I always get "Not found" error. Already looked to some related posts here but none was able to fix the issue.  1. [GET] to https://{shop}/admin/api/2023-01/orders/{order_id}/ful...