If QuickBooks won’t switch to multi-user mode, network misconfiguration or disabled services may be the cause. Confirm the server hosts the company file and that QuickBooks services are active. Review folder permissions, allow access through the firewall, and ensure all systems use the same program version. Restart the server and workstations to reestablish seamless multi-user access.
Also read:- https://asquarecloudhosting.com/quickbooks-multi-user-mode-not-working/