@UltraWorlds - I am having the same problem and have no idea how to fix it in the bloody editor.

I can't register my players to the league (5th division), apparently because they're on amateur contracts. Is it supposed to be like this?

Just keep trying to verify, the editor throws up random error messages sometimes but if you try 3-4 times you should be good. If that doesn't work then verify each division individually

Then I try to make changes in this db file and verify it afterwards I get required teams error for league 1 cup. Possible to fix?

super

I think wikipedia, and I can then review it and tell you what is right/wrong?
https://en.wikipedia.org/wiki/2020%E2%80%9321_Super_League_Greece
https://en.wikipedia.org/wiki/2020%E2%80%9321_Cypriot_First_Division

Do you know any good websites for them that lists all competitions and clubs? including regional/amateur leagues?

will you do cyprus and greece please?