The 2 different API-keys for facebook-messaging (previously located in bundle c.o.messaging.facebook at /conf/facebookmessaging.properties) and facebook-contacts (previously located in bundle c.o.subscribe.crawler /conf/crawlers/facebook.yml) are consolidated into one:
This API-key is found / needs to be set in bundle om.openexchange.oauth.facebook at /conf/facebook.properties.
The two parameters are com.openexchange.facebook.apiKey com.openexchange.facebook.secretKey.

These are set to the key for the domain open-xchange.com per default and need to be set individually for each servers domain. The creation of the necessary facebook-application is documented at http://www.facebook.com/developers/ (facebook account required).
Please make sure that the applications settings includes the servers domain as Site