This usually happens when your DAW is unable to connect to the license server. This might be caused by software like Little Snitch, LuLu, GlassWire, the Windows Firewall or other firewall/privacy software. It's important to understand that when you prohibit your DAW from connecting to the internet, then none of the Plug-Ins will be able to connect as well. This is because the DAW is the main executable in this scenario (if plug-ins are isolated, it may be a process which is separate from your DAWs process).
The easiest way to resolve this is to use the standalone version of the plug-in and activate and lock the license to either your computer or to one of the supported USB dongles. Once a license is locked, no connection to our license servers is required anymore. More information about our license system can be found here.
Alternatively you can also use the offline activation method - but it is a bit more involved and the end result is the same.
The workaround might actually be a viable solution in most cases. But only full licenses can be locked. So if you're getting this error while running the trial version or if you don't want to lock your license for some other reason, you need to identify who is blocking the connection and at least temporarily permit Your DAW to connect to the internet.