Problem:  

BookNow button is missing from Facebook Mobile

Cause:  Facebook presents a completely different layout and many of the buttons are missing on mobile, such as "Timeline" "About" "Photos" as well as BookNow.

Next Steps: This is a limitation of the Facebook mobile platform, as they opted not to include those buttons on their mobile version.  Thankfully, your website information is posted on the mobile home page - be sure that your website is listed in Facebook and that you have the BookNow button setup on your website.