Facebook "Send to messenger" button not displaying

Question

I cannot get the "send to messenger" button to display to the user.

1) Facebook SDK is installed correctly as other plugins are displaying and working 2) I'm logged in as an admin of the page and of the app on Facebook 3) The app has messenger permissions for that page 4) The public HTTPS domain is whitelisted with that pages messenger platform.

Answer 1

I had left the "data-ref" as the default which was '", by removing the "<" and ">" symbols it now works fines.