Error when trying to install Passwords via Nextcloud admin backend

Dear all, i get an error right away when i try to install:

"cURL error 35: OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to git.mdns.eu:443 (see http://curl.haxx.se/libcurl/c/libcurl-errors.html) "

The Nextcloud 18.0.4 installation is fresh and running on a standard webserver where we can use other nextclouds.

Any ideas? Thank you!