onlyoffice-owncloud: I cannot Edit files with Onlyoffice and Nextcloud 12 and Onlyoffice App 1.0.5

Hi

Since many hours, im trying to get onlyoffice working with nextcloud. I have onlyoffice running as a docker container on port -p 444:443

I also run an apache as reverse proxy.

here is my configuration:

` <VirtualHost *:443>

    LoadModule setenvif_module modules/mod_setenvif.so

    ServerName abc.domain.com
    SSLEngine On
    SSLProxyEngine On
    ProxyPreserveHost On
    ProxyRequests Off
    SSLProxyCheckPeerCN off
    SSLProxyCheckPeerExpire off
    SSLInsecureRenegotiation on
    SSLProxyVerify none
    SSLVerifyClient none

    SSLProtocol all -SSLv2

    SSLCipherSuite ALL:!ADH:!EXPORT:!SSLv2:RC4+RSA:+HIGH:+MEDIUM

    SSLCertificateFile      /etc/letsencrypt/live/abc.domain.com/fullchain.pem
    SSLCertificateChainFile /etc/letsencrypt/live/abc.domain.com/fullchain.pem
    SSLCertificateKeyFile   /etc/letsencrypt/live/abc.domain.com/privkey.pem

    SSLProxyCheckPeerName off
    #RequestHeader unset Accept-Encoding
    #ProxyPass / https://192.168.50.20:444/
    #ProxyPassReverse / https://192.168.50.20:444/

    RequestHeader setifempty X-Forwarded-Proto https
    ProxyAddHeaders Off

    ProxyPassMatch (.*)(\/websocket)$ "wss://192.168.50.20/$1$2"

    RequestHeader unset Accept-Encoding
    ProxyPass / https://192.168.50.20:444/
    ProxyPassReverse / https://192.168.50.20:444/
    #ProxyPass "/websocket" "ws://192.168.50.20:444/websocket"
    #ProxyPassReverse "/websocket" "ws://192.168.50.20:444/websocket"

    <proxy *>
            AddDefaultCharset off
            Order Allow,Deny
            Allow from all
    </proxy>

</VirtualHost> `

Unfortunately, i alway get the following image:

I defenitley dont havy any more ideas. I would be very happy if someone could help me.

Thank you.