I know that's a bit old topic, as I've researched, but those, what I've found were all outdated.
So the problem in a nutshell: I click on Upload World, select my .zip file, it says uploading, no error messages, I start the server, and I'm not in the "uploaded" world. I've also tried it with a world what I've downloaded from there, but it didn't word neither.
What could be the problem?
Server specs:
version: 1.16.5
software: spigot
plan: free
Thanks in advance!