Instagram API prevents redirection to iOS app upon successful login

I'm trying to integrate Instagram login into my app to get the logged in user's details, I've registered my app on Instagram and got my client ID, then I added a new URL Type in the project settings with the identifier: igxxxx (where xxxx is my client id), i've also set the redirect URI to be (xxxx://authorize), once I successfully log in (using a webView) Instagram displays a white blank page with (400 Bad Request) text written on top, however, when I change the redirect URI to anything else, it opens without problems after a successful login.
how can I redirect the user to the app after he logs in with Instagram.

p.s. I use this library to ease up things.

thanks in advance.