Changing User Licenses From API?

I'm not sure what you mean by 'License' as we do not use that term in our API. If you mean to find features that are available for a user, you can get those programmatically by calling 'Get User Features API' : https://developers.ringcentral.com/api-reference/Features/readUserFeatures . Not that this is READONLY meaning you can't alter the features programmatically but only read them. Hope this answers your question.

There is no API to change user licenses. You must delete the old user and create a new user accordingly.

If I wanted to provision a user with Mobile license only, what's the best way to do that?