So I can already use the API to create a new user in my Sandbox environment successfully, and assign a currently unassigned extension/phone number to that user.
Let's say then, that I run out of unassigned extensions. Is there a way to "buy" or add a new extension/phone number from the API? There is a "Create Extension" API endpoint, which I assume would do what I need? Will it automatically update the billing cycle with the new extension added to it?