I'm dealing with this too. My submission was rejected because I 'didn't attach the subscriptions to my v1.0'. But I never saw that section. (I have 3 other apps live on the App Store with subscriptions for about 1 year, never had this issue).
Anyway, after getting this rejection for 'not attaching', I still don't see the section for attaching it. Tried pretty much all that OP said, and had the same results.
Finally, just now, I submitted a new build for v1.0, after removing all paywall and subscriptions for my app. Hopefully this free version will get approved and I can later go ahead with a v1.1, where this section might show up.
Extremely frustrating.
Topic:
App Store Distribution & Marketing
SubTopic:
App Store Connect
Tags: