Why can't I reply to a Facebook message in Inbox?

  

Facebook’s Messenger Platform Policy provides the following reasons for receiving the error message Unable to send Facebook message when replying to a Facebook message in Inbox:

  • The Facebook user left a comment on your Page or sent you a private message, and you did not reply within 7 days of the user's most recent communication.
  • The Facebook user blocked or muted your conversation.

For more information, see Facebook’s Messenger Platform Policy Overview.