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 is an easy way for developers to obtain authorization to make calls, send text messages, purchase phone numbers, read access logs and perform other API functions on behalf of another Twilio project owner.
This service lets users buy their own Twilio credit so that there is no cost to you, the developer, for their Twilio usage. You prompt customers to create Twilio Connect projects, and they pay for the time they spend on the phone from those projects of their own.
As an example, imagine you want to create an application that allows your customer to forward phone calls. You could do this, have the usage billed to his or her Twilio project, and also access his or her logs to provide detailed call analytics.