After a long wait, the Messenger chat bubble is finally here on iOS.
How can I enable this feature? Invite you to follow the following article
Turn on the bubble chat Messenger for iPhone very simple
First, you need to update Facebook and Messenger to the latest version
After successful update.
Please access the Facebook application.
At the main screen, you choose to go to Menu (icon 3 dashes) located in the bottom right corner of the screen
Scroll down to Notifications >> Messenger Notifications
In the Notification window via Messenger, tick Chat Bubble.
Thus, you have successfully enabled the Messenger chat bubble feature
Note: This feature is being updated gradually by Facebook by account, so if you have not been able to do step 3 and step 4 of the above instructions, then you will patiently wait for a short time.