Can't Login to the Plesk Repair Kit

Hello my problem is this:

I can login at my plesk, so that means my credentials are ok.
But when i go to
https://MYSERVER:8443/repair/
The window asking my credentials pops up, I input the same credentials as the ones I use in plesk.

Then it thinks for a second and asks the credential again.

No error or something else.
I used all browsers to check if it is a browser thing.