discussed that today - they include:
Using Messenger for Customer Service
Promoting Your Business with Messenger Usernames, Links, Codes, and Greetings
I vaguely remember the "messenger code", aka:
"To get the messenger code, go to your Facebook page admin and look for the message inbox. You should find a round-shaped icon at the bottom left-hand corner containing the code.Are you using this?
When you click the icon, a screen appears that presents the code, an option to download it, and a quick demo of how it works.
You can share your code with fans and followers using it as your profile image, in a page post, on your website, in an ad, on business cards, store signage, or just about anywhere you can think of."