First get a valid license from ProLib Tools GmbH or any other AFP distributor world-wide and you'll get a personal license file - AFP3.LIC - via email. Normally this happens after the bill is registered as paid but it is always wise to call the distributor directly and talk with them in case of emergency...

Store the sent AFP3.LIC file in your AFP3 application directory ie. C:\Program Files\AFP3 .

Second, launch the AFP 3.0 ControlCenter, load your current configuration file (normally afp.config) and change to tab "License".
Now, check if the license is correctly registered to you or your customer. Ensure that you have a connection to the internet and click on the button "Activate" to request an activation key for your machine.

The activation process sends your registered username, the serial number and the hardware key per HTTP protocol to one of the Web servers of ProLib Software GmbH and you'll get a valid activation key back.

Afterwards, the activation key shows up in the status list at the left bottom and the status indicator should be 'green'.

Quick restart of AFP 3.0 and... Bingo! Your AFP 3.0 is now activated.

Enjoy it!