How do I fix QuickBooks multi-user mode not working?

I faced this issue while working remotely with a client last year. The problem was mostly related to network settings and permissions. First thing I checked was whether the hosting was enabled on the server system only; this is a common mistake. Then I ran the QuickBooks Database Server Manager, which helped detect the issue. Firewall settings were also blocking access in our case, so we had to allow QuickBooks ports manually. Restarting the QB services also helped. Honestly, it sounds technical, but most fixes are simple if you follow the steps properly. If nothing works, updating QuickBooks to the latest version can also solve hidden bugs. That worked for us eventually.