I have 2 aplications with the same problem. Apple i not acepting the app with subscription enabled.
The older one is called TeMuKi. It is bind to the Adobe account email@example.com.
The new one is called iMAJA, it is not available in appstore, because it has the subscription option buidt in from the beginning.
It is bind to the Adobe account firstname.lastname@example.org. There is only one folio available in that acount.
The error is.
Server Communication Problem
Your subscription was successfully purchased. Unfortunately we encountered an error while determining which issues are available for download. Your subscription will be applied the next time the library successfully updates.
For retail folio product IDs, you specify them on the Adobe side when publishing the folio, as you've done. For subscription duration product IDs, you specify them in Viewer Builder. See the companion guide PDF.
When you're switching from a multi-folio app to a subscription app, you need to re-create your viewer in Viewer Builder. That means creating a new instance of the viewer. And remember to specify your shared secret using the account admin tool.
Of course, i am not 100% sure. But i think my problem was with Apple shared secret.
I copy-pasted it from Apple inapp purchases to the Adobe digital publication account shared secret field, and i think, there was an extra space in it. Adobe dont show the string you paste.
So at first i pasted it to notepad, checked that all data is correct, and then from notepad to the Adobe digital.
And it worked. Not at once. It took some hours, but next day it was OK.
My advice: do not directly copy-paste those keys to Adobe, use text editor to check your string.