Before Authorizing a Connect App
In order for a customer to authorize your Connect App they must have previously created and upgraded Twilio account.

Twilio Connect allows you to request two different levels of access from users of your application: "Read all account data" or "Charge account for usage."

Once you create a Connect Application, Twilio will give you a snippet of HTML to drop into your page which will display a "Connect Button" on your webpage. This will enable users to authorize your Connect App to use their Twilio project. If your user doesn't yet have a Twilio project, Twilio will prompt them to sign up.