Facebook‘s message to banks at Money2020 in Las Vegas yesterday? Your customers are here — engage them here.

And bank customers are on Facebook. Everyone is. There are now 1 billion people who use the network, said Deborah Liu, director of product management for platform monetization. She was being modest. It’s closer to 1.15 billion, but who’s counting?

Liu also mentioned that Facebook has 800 million mobile users.

She began the Facebook payments story by describing developer payments, later known as Facebook Credits. Facebook paid developers more than $2 billion in credits in 2012. Credits has since been shuttered in favor of more than 80 payment methods now available on the social network, Liu said.

In May, Liu said, Facebook created a Payments Growth Team, tasked with bringing more payments into the network. (When Facebook creates a “Growth Team,” look out.)

Liu described in detail the testing that went into perfecting forms for entering payment information and how small tweaks affected consumer behavior. But the upshot is that Facebook needs more credit card information from its users to make payments smooth and seamless inside the network.

Mobile device users spending 80% of their time inside apps, as opposed to on the mobile web, Liu said. This siloing of experience is problematic for the mobile experience, as apps generally discourage horizontal movement to other apps. It’s also difficult for new apps to gain traction. Here Liu addressed the bankers in the room, making a direct pitch to advertise their bank apps on Facebook. “Your users are on Facebook,” she said.

The payments goal for Facebook is that users will be looking at their feed, see a product in a sponsored post or a friend’s post, move from the news feed to make the purchase — still within Facebook — then return to the news feed. But for this work, Facebook needs more payment and address information. This information can be had through games and Facebook apps, and the Payment Growth Team will doubtless have more good ideas in the coming months.

Money2020 was all about new possibilities in the payments space. At the Bank of America-sponsored tweetchat breakfast Wednesday morning, several participants mentioned Apple, the elephant in the room in conversation after conversation about the big non-FI players getting involved in payments. Dave Birch of Consult Hyperion observed, “Payments is a low-margin business. Why would Apple want to get involved in payments?”

Why indeed?