This usually indicates that you and the person you are attempting to message are not connected as Facebook friends.It might be due to various reasons like
- You have sent a friend request but they have deleted the request.
- One of you has blocked the other person on Facebook.
- They have set privacy settings on Facebook for that action.
Source: My Youtube Channel (https://www.youtube.com/watch?v=wOGw008A19Y)
Let's look at one of the scenarios:
Suppose you've sent a friend request to someone when they receive the request they have two options they can either accept the request or delete it if they choose to delete the request as shown below
fig. Delete / Confirm option to accept or reject Friend Request
and later on, when you start to chat with them through Messenger you'll receive a message stating that you are not friends on Facebook.
If you get a screen as shown below
fig. "You are not friend on Facebook" message when you initiate chats in messenger
then you can send messages with emojis and more also the receiver will receive the messages furthermore the recipient can modify their settings to prevent you from sending any messages even if they have deleted your friend request and the reason for this chat feature exists even not friend in Facebook because Messenger wants to encourage people to connect with each other on messenger even if they are not friends on Facebook sending this notification can both help people find and connect with each other by reminding them that they have the ability to talk with people without being a friend in Facebook and messenger.
Note: Based on the setting set by the recipient they can make you hide their Feed, stories and photos, and profile from you.
Ans: This is because the recipient has set their privacy settings to allow non-friends to send messages. It might also be the case that they have blocked you from seeing their profile but not from sending them messages.
If you want to play with these privacy settings then follow the below steps:
- The "Settings" tab is located on your Facebook profile, so click there.
- Select "Privacy" from the menu on the left.
- To access the "Who can send me messages?" option, scroll down.
- The default choice is "Friends," but you may alter it to "Everyone" or "Specific friends" if you wish to accept communications from people who aren't friends.