You pay a one-time fee for the software. It includes 12 months of maintenance (updates and support). You can renew maintenance annually.
Once you purchase a commercial license key, you must apply it to your PRTG core server instance to unlock your sensor quota. Step-by-Step Activation Guide prtg network monitor license key
License Name: John Q. Public License Key: 0223515-FFSEJC-ZHGRDFM-UR1CS8-U73FGK-G645F2-YVF1DD-H8323N-D11HG9-M2DRG You pay a one-time fee for the software