Fails to apply the update patch

when we are trying to update our app using a patch, we are facing some issues and instead of applying the patch, it downloads the full build as the update.

on further checking we found that it displays the message "Canceling Update" and after that it downloads the full update 🙁 🙁 🙁

please help us out how we can solve this and also we are planning to purchase this software as soon as our issue is resolved.