In some cases, you may not even see certain read receipt icons. Instead, the words "Sending," "Sent," or "Seen" may appear below your last message to indicate the corresponding status.

Now click the message and Facebook Messenger will mark it as read. Log in to the Facebook mobile app and you should no longer see the unread message icon.

This article explains why Facebook Messenger is not sending messages and what you can do to fix it. These solutions can be ...