Cause: Client version mismatch. The Pro server requires a Pro client to use sync features. Fix: Download the latest client from the official website. The free client from GitHub will connect but will not show the Address Book tab.
To make it survive reboots, use NSSM (Non-Sucking Service Manager). rustdesk server pro license key install
Before touching the license key, ensure your infrastructure is ready. Cause: Client version mismatch