Facebook callback URIs do not seem to like question marks so one cannot generate a token unless clean URLs are enabled.

Perhaps it would be possible to add a message to this effect on the status report, or abort an attempted installation if the clean_url variable is not equal to 1.

The message emitted when token generation fails does not lead one to suspect that the redirect URI is invalid so I can see others spending alot of time on a simple fix, as I did.