PHP7 - server error?

Hello, maybe someone can help me. My Nextcloud 11 is with a host on the server, therefore, only limited access. Since the transition to PHP 7.0, Nextcloud no longer works. The following messages:
External server error
Bad gateway
Both messages appear alternately with the settings.

Does somebody has any idea?

Nextcloud itself is compatible with php 7.0. Bad gateway and external server error could indicate a configuration issue on the webserver, you need to check your server or ask your hosting provider to solve this problem.

Yes I have had problems with 7.0 too
I met all the recommendations not just the minimums, so I expected it to work.

In your logs does it say anything regarding a Header issue?