If you have recently updated Mafia Wars Addon you may have noticed some Great New Features! And some of them need permission to work.
First you need to "Give Permissions" to the addon to access certain features of FB, it just needs permission to read the feed and make posts to the wall, groups, etc. Then you need to update your key, which is essentially just your mafia wars credentials so it knows its your account its using. And if you don't want to have to update the key 30-60 minutes ( it will pop-up an update window if it tries to use a feature and the credentials have expired) you can click "endpoint long-lived key" which is more of a permanent option and so far I haven't been asked to update it again, but I'm sure it will eventually.