Just like with the one-on-one payments feature, all you need to do to get started is to hook up your Facebook account with a debit card, which you can then associate with a PIN to authorize your payments. Now when you're in a group conversation in Messenger, you can tap the Payments icon (which you can find by tapping the plus sign in the bottom left corner). From there, choose the folks in the convo that you want to either send or ask money from, enter in the desired amount plus an accompanying note, and send it off.
If you're the one requesting money from a group of friends, you can either enter in the desired amount per person, or you can enter in a total, and the app will automatically divvy up the per person amount for you. From there, you'll be able to track who has paid and who hasn't.
The service will be available for free for all Messenger users in the US and will be available for both iOS and Android. Now that it's so easy to pay up, it's time to tell your buds their freeloading days are over.