If you are looking to block a pesky or chatty contact on Facebook Messenger, the app offers a very simple way to do so.
After blocking someone on Facebook Messenger, you will appear as "invisible" in their contact feed. The user will no longer be able to see when you are online, and they will no longer be able to call or message you. In addition, Facebook Messenger will notify you each time that you attempt to join a group conversation that involves any of your blocked contacts.
How To Block Someone on Facebook Chat
N.B. Blocking someone on Facebook Messenger is NOT the same thing as blocking somebody on Facebook. Unless you completely block a contact, blocked Messenger contacts will still have access to your Facebook profile and all of its platform functionalities.
Open Facebook Messenger, and search for a conversation with the person who you would like to block.
Tap the small blue exclamation mark displayed at the top-right corner of your screen to display the Details page. Then, tap Block:
Next, toggle the Block Messages switch ON:
Your contact is now blocked on Facebook Messenger.