If you think it will be easy to use Instagram API you are a fool!
Lot of process to review your application.
Lot of constraints.
In sandbox mode you will have only access to your user and his data.
So a lot of endpoint won't work as expected in documentation.
Currently I will try to get all permission for this works, BUT if I can't I will stop developpement for this dead API
Bot for Instagram
Callback URI must be exact with what you declare.
Here the authorized callbacks