This document could not be saved - Onlyoffice

Seafile Server
1

I was able to get OnlyOffice running, but there is still a small issue. When I open a document, a popup appears saying, The document could not be saved…

However, I can still edit the document, and changes are being saved properly. Downloading files in OnlyOffice also works correctly. Everything functions as expected, except for the popup.

My seafile instance is running at https://seafile.mydomain.com
All traffic for onlyoffice is routed at https://seafile.mydomain.com/onlyoffice
Im using Seafile v12 and nginx. I’m not using Caddy.

ONLYOFFICE_APIJS_URL is set to https://seafile.mydomain.com/onlyoffice/web-apps/...
ONLYOFFICE_JWT_SECRET is correctly configured.

This is part of my NGINX configuration:

location /onlyoffice/ {
        proxy_pass         http://127.0.0.1:6233/;
        proxy_http_version 1.1;
        proxy_set_header   Upgrade $http_upgrade;
        proxy_set_header   Connection 'upgrade';
        proxy_set_header   Host $host;
        proxy_set_header   X-Real-IP $remote_addr;
        proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header   X-Forwarded-Host $server_name/onlyoffice;
        proxy_set_header   X-Forwarded-Proto $scheme;
        proxy_read_timeout  1200s;

        # Logging
        access_log /var/log/nginx/onlyoffice.access.log seafileformat;
        error_log /var/log/nginx/onlyoffice.error.log;
    }

When changing onlyoffice to onlyoffice.mydomain.com, adjusting ONLYOFFICE_APIJS_URL and nginx configuration, I dont get the popup.

What could be the problem?