When the online subscription has not been validated yet, the NoMachine server issues a message like:

 "License is not activated. Please activate it using 'nxserver --subscriptionset'.

The command proposed is not complete, path to the license file is missing.

Message should report the proper format of the command:

Subscription is not activated. Please activate it using 'nxserver –subscriptionset <path to subscription>'

For example, if the server.lic file is in the same directory, you will need to run:

'nxserver --subscriptionset server.lic'

Additionally server usage for the command can be also improved to have:

--subscriptionset  <subscription>  [--target <uuid>|<node:port>]

  Deploy the subscription on this host, where <subscription> is the
  license file or path to the license file if it is not in the current  
  directory. In case of a cloud server or Enterprise Terminal Server,
  use --target <uuid> to deploy the subscription on the given node
  specified by its uuid or node:port.