Switching plugin license from Craft 2 to Craft 3 Dumb question, but...

I purchased a plugin when using Craft 2 and now I'm trying to input the license for it in Craft 3. There's an input for the license key when I go to settings -> plugins, but the submit for it says "buy now" and tries to put the plugin in my cart. How do I give Craft 3 the license?
That's a question for the plugin developer. If the plugin isn't purchased through the plugin store, then each developer is responsible for generating Craft 3 licenses on their own.

It's probably safe to say that your Craft 2 license number is not going to match your Craft 3 license number. Contact the plugin's developer for more information.