Finextra:
British Facebook users can now send money to each other through the social network giant’s Messenger app. Facebook has got all the major UK banks and card firms onboard for the service’s first foray outside of the US, where it launched in 2015.

To send money through the free new feature, users press the blue plus symbol within a chat and select the payment option. The first time a payment is made, people are prompted to add their debit card details and then enter the amount they want to send.
Source