In my case Apple rejected subscriptions, the answer from Apple was:
We were unable to find the following required item(s) in your app's metadata:
– A functional link to the Terms of Use (EULA)

What helped in my case:

1)
Created custom Terms of Use (insread of standart Apple EULA).

2)
Added links to Terms of Use and Privacy Policy to App Description field:
appstoreconnect / app / Distribution / iOS App / version / Description
(or just https://appstoreconnect.apple.com/apps/\[appid\]/distribution/ios/version/inflight -> Description)
My links in Description field look like that:
...
Terms of Use: https://...
Privacy Policy: https://...

3)
Added a plain text of License Agreement instead of it's url to "Custom License Agreement" field:
appstoreconnect / app / Distribution / General / App Information (or just https://appstoreconnect.apple.com/apps/\[appid\]/distribution/info) / General Information / License Agreement / Edit / choose "Apply a custom EULA ..." / Custom License Agreement
Instructions for this point:
https://developer.apple.com/help/app-store-connect/manage-app-information/provide-a-custom-license-agreement

I'm not sure about what exactly solved the problem, but I think the point 3 was the main reason.