I had similar issue and this is how I fixed it.
You have to uncheck the "Disable implicit OAuth:" by going to :
-> Manage Clients
-> Click edit on the app/webapp.
-> Uncheck - Disable implicit OAuth:
-> Update the settings and try to run it again by going to the link :
https://api.instagram.com/oauth/authorize/?client_id=CLIENT-ID&redirect_uri=REDIRECT-URI&response_type=token
In the link, replace the values that were provided to you and in the response_type, give value as token to get the access token and if you want to get the request code, just replace token with the code in the URL.
Hope this helps for you and for future viewers.. Good luck.. :)