@Jazzy232 I think I might have found a solution. I've cancelled my old review submission altogether in order to release the version I wanted to submit. Afterwards, I've added this new version to a new review. Then, went to Subscriptions and added both the Subscription Group and the individual subscriptions in the same submission and then I could submit all of those together. Now instead of only the app (1 item), I have (in my case, 1 app, 1 subscription group, 2 subscriptions plans) 4 items in "Waiting for Review". If that is the right way of doing it (cancelling the old submission), I don't know. But now it seems it went in the format Apple expects for a first submission. Good luck!

I'm having the same issue.