The map isn't working with my set port and the server adress. I am running a Paper server which should be able to run spigot and bukkit plugins.
I read that I need to set an API version in a plugins.yml file. But I can't find such a file anywhere on the server. What do I have to do exactly?

Hi, thanks for the reply and your time. Luckily, I found a solution. Sort of.
I pay a host. MCProHosting.
I managed to partially solve the issue. But a new one occured.
I have no idea about coding etc but I managed to find the plugins.yml file inside the .jar file of the plugin. I added api-version = 1.16 and it worked. :D The server console sais that the plugin is working correctly. Now the new problem that occured seems to be a problem with MCProHosting itself.
I opened a port on the server (the same that I set as webserver port in the plugins config file), so people can access the map in their browser. But as soon as I tell MCProHosting to open any port besides the main port for the server, everything crashes and the server won't start up again, even when I undo all the stuff. I basically have to reinstall the server.

hey, do you have a host, or do you host on your own computer?
That api version is not mistake on your side, it's in plugin's code and it should't cause any issues.