SolarWinds NTA informs you that you are running an evaluation version, which has not been licensed yet.
Your SolarWinds NetFlow Receiver Service Evaluation [receiver name] will expire in x days. Please contact SolarWinds support to purchase a licensed version. Thank you.
To resolve the issue, purchase a license and activate it. Your SolarWinds licenses can be activated directly during the installation process. However, SolarWinds also provides a powerful License Manager which allows you not only to activate your licenses, but also deactivate a license on a certain machine and re-activate it elsewhere.