You do not need an activation code to authorize licenses acquired through a subscription.
If you are prompted for one, it is very likely that the licenses you are trying to activate are deposited in an iLok account different than the one your iLok key is registered to.
This most likely happened because the licenses are deposited in the iLok account Gobbler created for you during the sign-up/purchase process, because you did not provide one at the time, instead of in your pre-existing iLok account.
Please see this article to remedy the issue.
The Gobbler Team