In order for the MindMixer and Facebook sync to properly activate, check that the Facebook account you're attempting to sync is a page, not an individual's Facebook account. It's possible that when you are adding the Facebook page to your account settings, you selected "skip". That prevents the Facebook page and MindMixer site from syncing.
Note: You are required to be an administrator or have login credentials to the Facebook or Twitter account you are trying to connect.
For details on how to sync your Facebook and Twitter accounts to your MindMixer site, visit this article.