Ensure you aren't trying to use a V2.3 key on a newer version (like V2.4 or V2.5).
They typically offer various tiers based on how many "Technician Seats" or simultaneous connections you require.
Your firewall might be blocking the software from reaching the activation server.
A stable connection is required during the initial "Enter License Key" process. Conclusion
USB Redirector Technician Edition is designed specifically for professionals providing remote maintenance services for USB-based hardware. Unlike the standard version, the Technician Edition allows the technician to act as a "server" that can receive connections from multiple "clients" (customers) simultaneously.
Before committing to a purchase, you can use the trial version to verify that V2.3 is compatible with the specific USB devices you intend to service. Troubleshooting Common Activation Issues