Make sure that you and the users you connect are using the free version of TeamViewer.
If you use TeamViewer for personal use only, here’s how to fix the TeamViewer trial expired problem. Paid (commercial) version - the number of connected devices and the duration of the sessions are unlimited.Free version (non-commercial use) - designed for home use and connecting to a small number of remote devices.
TeamViewer Versions: Trial Expiration Problem
