Mattermost Websocket handshake fails when using apache as proxy

I'm not making any progress with my Mattermost installation on my server. I've installed everything without any problems. After that I've enabled the apache mod proxy_wstunnel and added the following directives in my Plesk domain for additional directives (it like ` or `): **HTTP:** ErrorLog ${APACHE_LOG_DIR}/mattermost-error.log CustomLog ${APACHE_LOG_DIR}/mattermost-access.log combined # Enforce HTTPS: RewriteEngine On RewriteCond %{HTTPS} !=on RewriteRule ^/?(.*) https://%{SERVER_NAME}/$1 [R,L] **HTTPS:** ServerName mattermost.xxx.de ProxyPreserveHost On # Set web sockets ProxyRequests Off RemoteIPHeader CF-Connecting-IP RewriteEngine On RewriteCond %{REQUEST_URI} ^/api/v[0-9]+/(users/)?websocket [NC,OR] RewriteCond %{HTTP:UPGRADE} ^WebSocket$ [NC,OR] RewriteCond %{HTTP:CONNECTION} ^Upgrade$ [NC] RewriteRule .* ws://127.0.0.1:8065%{REQUEST_URI} [P,QSA,L] RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f RewriteRule .* http://127.0.0.1:8065%{REQUEST_URI} [P,QSA,L] RequestHeader set X-Forwarded-Proto "https" [0-9]+)/(?users/)?websocket"> Require all granted ProxyPass ws://127.0.0.1:8065/api/v%{env:MATCH_APIVERSION}/%{env:MATCH_APIUSERS}websocket ProxyPassReverse ws://127.0.0.1:8065/api/v%{env:MATCH_APIVERSION}/%{env:MATCH_APIUSERS}websocket ProxyPassReverseCookieDomain 127.0.0.1 mattermost.xxx.de Require all granted ProxyPass http://127.0.0.1:8065/ ProxyPassReverse http://127.0.0.1:8065/ ProxyPassReverseCookieDomain 127.0.0.1 mattermost.xxx.de But when I save this, restart apache and go back to Mattermost, I'm still getting the Websocket error: In the network tab the response is empty....