If MassageBook is notifying you that you do not have a Facebook business page even though you do, completely sign out of Facebook on whatever device you are using to connect and disable any pop up blockers that are turned on in your browser.
Afterwards, navigate back to the Facebook Connect page within your MassageBook business account. Select the Connect button, and a small window will appear for you to enter your Facebook login credentials. Business pages are associated with your personal account, so you'll be entering your personal login. Be sure to grant access to the Apps section. That will allow the Book Now button to display on your business page. Your Facebook business should appear as the option to connect to at the end of the process.