Facebook OAuth2 is a feature I frequently integrate, but sometimes its error messages can be downright opaque. In particular I keep on forgetting to associate my Facebook account on applications where Sandbox Mode is enabled. The error message in this case is the following: Sorry, this feature isn't available right now: An error occurred while processing this request. Please try again later. This message is super cryptic, since what I usually need to do is to register my account as a tester or admin on the Facebook application page. If you get this error message here are the steps to fix it: As an application administrator, go to the OAuth2 configuration page for the application in Facebook. Add the Facebook account as an admin or tester on the "edit roles" screen. This will send an application request to that account. As the added account, accept the application request to become an admin or tester. At this point the Facebook login should work for the accou