How to specify callback URL in this library?

[ally9335]

Steps to Reproduce

I've gotten an error "Callback URL not approved for this client application. Approved callback URLs can be adjusted in your application settings (Code 415)"

Right, in my Twitter app it's perhaps not what what this library expects. But how to specify the callback URL here, for this library, though? This isn't mentioned anywhere in the README

Expected Result

Actual Result