Hey there.
So, imagine you have a B or C team, or a u19 team that dosn't participate in any national league, the game should invite it to participate in the lowest division possible just before the calendar generation.
Here is an example:
I'm currently in 2030 with KFA 🇮🇸, and my youth team only do some friendly matches, boring. i'm also aware that this is an "DB mistake" but i think this would be so simple to workaround by simply add extra spots for that division. In this case, that woudn't be necessary, since there's an empty 8th spot in the second group that could be ours.