Use the provided key during installation. For the first 30 days, you can use an unlimited number of sensors to test your entire network. Paessler Blog Step 3: Automatic Downgrade.
(sufficient for approximately 10–20 devices) free of charge forever. How to Get Your Verified Key Free Network Monitoring software with PRTG - Paessler prtg network monitor license key free verified
Visit the official Paessler download page to get the trial installer. Use the provided key during installation