Previously, Messenger only supported payments via debit card. Ironically, Messenger is adding support for PayPal before popular transaction app Venmo which is owned by PayPal.
Messenger is also adding a feature that will let you receive notifications about recent PayPal transactions.
Facebook has slowly but surely been turning Messenger into a full-fledged business of its own, and the ability to send and receive transactions was just one small part of that process. PayPal is just another option on the table.
PayPal transactions are beginning to roll out in the US others today; no word on when it’s arriving in other countries.