Help! Can´t access anymore. No coding experience

For EU project we were using Nextcloud to store and share data.
It worked two weeks ago. Today we all receive: HTTP Error 500: Diese Seite funktioniert nicht kann diese Anfrage momentan nicht verarbeiten.

We used to access via:

Can someone help us get our data back?

I think you better reach out to our admin… there is a contact button on the site hopefully you reach the tech representative there as well.

BTW: you should not use plain http:// in the internet…

Because of the url of your Nextcloud it seems that you use your webspace (subdir and database)) for your Nextcloud. That is not the best possibility for a Nextcloud installation. Your host seems to be HostEurope. Ask the person who installed the Nextcloud fore details. Mostly it is better to use a Managed Nextcloud. But it seems that HostEurope does not offer it.