If you're receiving an error stating that your Facebook fan page is invalid, it is most likely due to one of two issues:
1) Your Facebook page is not available to all ages.
2) Your Facebook page is not available to all countries.
To connect your Facebook business page, you will need to navigate to your settings for your business' Facebook page, and make the page available to all ages (13+) and/or make it available to all countries.
If you continue to receive an error after completing the above actions, please reach out to firstname.lastname@example.org