I tried to upload my app build to the appstore but it got rejected for this reason: We discovered one or more bugs in your app. Specifically, we received an error when attempting to make in-app purchase. Please review the details below and complete the next steps.
Hey, I had the exact same issue a few weeks ago. One thing I noticed on the iPad version is that when you perform a test subscription, the “continue” button wasn’t visible on the screen unless you scroll down. So to Apple it looks like you can’t make the subscription.
I did a screen recording on my iPad and included in the notes that this was possibly the issue.
Resubmitted and it got accepted. Hopefully it’s the same easy fix for you.