While mobile advertising revenue drove Facebook to a banner first quarter, it is the company’s payments performance that is now taking center stage — and remains a bit of a bugaboo.

FB payments revenue, including “fees,” dropped to $237 million last quarter from $241 million in the last quarter of 2013, although it is 11.3% higher than 1Q13. However, Facebook, the world’s largest social network, explained that payments from games is an important component of its payments revenue, and the growth rate of those revenues dropped to just 1% from 8% in the last quarter of 2013. Here’s how FB explained it:

As we’ve discussed before, the shift to mobile is a significant headwind since our Games Payments revenue comes from desktop only, where usage is flat or declining, so growing this business going forward will be challenging.

That could be why payments was the very first question of yesterday’s FB earnings call, as Heather Bellini of Goldman Sachs & Co. asked “… Mark or Sheryl, if you can share with us your vision of payments for Facebook, and how the company might be able to play a role in reducing the friction that exists today when users are trying to engage in mobile e-commerce. …”

Sheryl Sandberg, the company’s COO, said that payments will generally support the developer activity on Facebook, and primarily as it relates to games. Sandberg said that FB will continue will that focus.

But Sandberg dismissed the notion that FB’s payments business is crucial to the company’s mobile advertising, which has been such a financial boon for it in recent quarters:

I guess really [it is] important to know that, our advertising business is very relevant for e-commerce and that doesn’t depend on taking payments and it doesn’t depend on a payment strategy because we provide a really great opportunity for marketers to find customers who are then going to go ahead and buy their products both online and offline.

Later, Sandberg completely shot down the notion that Facebook would be launching a peer-to-peer payments product, even though some press reports have it that Facebook is looking at building such a P2P money transfer service.

Sandberg: “We had our payments business for a while and we continue to have one and nothing new to apps there.”

No need for further clarification.