The pop-up window “Activation Code Entry” appears when opening/scanning the plug-in(s) for the first time. This routine is however only able to activate your license on one single computer.
You can activate Arché on up to 3 computers at once. For using the second and third activation, you will need to install and open iLok License Manager on each computer you want to activate the license on.
Read here to learn how the activation is done: Activating Arché with iLok License Manager