I've read quite a few question on stack overflow about that. this one and this one and quite a few others...
I've tried with and without encoding the redirect URI in the address bar . With and without https. With and without the final slash. And every combination of the above. I've triple checked the client ID.
http%3A%2F%2Flocalhost%3A9000%2F
http://localhost:9000/
https://www.facebook.com/dialog/oauth?client_id=272730539567323&redirect_uri=http%3A%2F%2Flocalhost%3A9000%2F
At some point, my code worked, And I logged in with it! Then I tried to change the redirection urls, and it never worked again, even after going back.
The worst is that I'm already logged in and you can see my name and profile picture on the screen !!!
I'm running out of ideas...
Note: I'm not including the actual code as I think it is irrelevant to the question and scala/play specific would only reduce the number of people trying to answer.