If you get the message "License Key is Invalid" here are the steps to resolve it.
If you just purchased the License key and you are trying to apply it to a version of FRP 6.5.3 or before the key will not work. Our license structure changed with versions 6.5.4 and forward. In this case only, email support and explain the above issue with a list of the key(s) that can't be used for this purpose so they can be de-authorized and exchanged for keys that will work with this version.
In all other cases when license keys will not apply....
1. Check that port 9100 is open from the server in question to the Management server.
2. Be sure the key is being pasted as one single line of plain text with no hidden line feeds, characters, or other formatting. to be sure there is no hidden characters you can copy the key from the email and paste it into notepad or other plain text editor then copy it from notepad to the license key box.
3. There is a possibility that you have mixed up which keys are already applied, try each of your keys on the server. If a key is in use you will find it is not accepted and the screen returns to unlicensed. There is no harm in trying each key, you will not be locked out. When the unused key is applied it will be accepted.
4. As a last resort you can open the /FileReplicationPro/etc/.key file (hidden file on Posix systems) and paste the plain text key string in on the top line overwriting what ever it already there.
Then restart all the frp services on the server. If you have more than one key to do in this manner do all of them then restart the FRPHelp and FRPMgmt service on the Management server only. It may take some time to show the new license status but the servers are licensed from the time you insert the valid and unique key on the server.