OwnCloud Desktop client

So the problem is:
I have setup the owncloud web version on cpanel and setup everything. The web client works fine. But now i installed the owncloud client for desktop windows 10 i fill in the website. Works fine but now i try to log in. I fill in my username and password and then click next. But then a red bubble pops up saying "Connection closed"

The first step to a solution:

We already run through all of that and it did not work

Then provide more information. Does native webdav work? Did you run the litmus tests against your webdav? Logfiles? Client version? Do you use external user backend? Do you use 2FA? ...

When you open a new topic, there is normally a template which guides you through some of these questions.