Messenger started making it easier to pay your friends for dinner back in 2015 when it introduced the option to transfer money in-app with a credit or debit card. If PayPal has always been more convenient, though, you'll love this collaboration: Facebook and the payment service have teamed up to give you a new way to split the bill. You can access the feature the same way you'd pay with a card. Simply tap the blue plus icon and then tap the green Payments button to bring up the two existing options.
If you'd previously set up the feature to pay using your card, just tap the Change button and choose Paypal to connect your account with Messenger. The feature is now live on iOS and will soon be available on Android. Unfortunately, you can only use it if you're in the US -- everyone else will just have to find other ways to spend their PayPal balance.