You are just filling the wrong login/pass data in.
You must not use your Otoy user login/pass pair to activate the Octane standalone and plugin.
After you got the subscription license - you have the license login/pass pairs shown in your Otoy user-area (in "Subscriptions"). Use the "OctaneVR for 3ds Max" license login/pass to enter it inside the 3ds Max, and use "OctaneVR" license login/pass pair to enter it into activation dialog of standalone.