PayPal Holdings (NASDAQ:PYPL) closed out 2020 with a bang when the company announced its fourth-quarter earnings last week. Revenue grew 23% year over year, while adjusted earnings per share climbed 29%. But it wasn't just the top- and bottom-line financial metrics that helped drive PayPal's stock price higher.

On this clip from Motley Fool Live, recorded on Feb. 4, "The Wrap" host Jason Hall and Fool.com contributor Danny Vena discuss some of PayPal's oft-ignored but equally important operational metrics.

Jason Hall: As much as the past several quarters have been good and investors might be thinking, well, can it really keep this going? Start peeling back the layers and you look at how much its opportunity is continuing to grow. Things like Venmo, all of it's other transactional businesses. Can you talk a little bit about that?

Danny Vena: Absolutely. The operational metrics for PayPal were just as strong as they have ever been, if not stronger. When you talk about the total payment volume, that's essentially the amount spent to buy stuff on the platform.

Hall: The total flow through PayPal, not their take.

Vena: Exactly right. That number was up to $277 billion up [LAUGHTER].

Hall: In the quarter?

Vena: In the quarter.

Hall: Last I checked, that's a run rate of about $1.1 trillion flowing through PayPal's systems on an annualized basis?

Vena: Right.

Hall: OK. Go ahead.

Danny Vena: That's a mind-boggling number isn't it? We're starting to talk Apple numbers here.

Hall: Right. [LAUGHTER].

Vena: Now. You mentioned Venmo. Venmo was responsible for about 17% of that total payment volume, amounting to about $47 billion, and that was up 60% year over year. Part of the thing that's driving Venmo was PayPal's decision last year to make Venmo a payment method that could be accepted by all of the merchants that accept PayPal. Now, instead of just being a way to split the check at a restaurant or a way for friends to send money to each other, now Venmo has become monetizable for PayPal, and obviously you can see from that number it has made a marked difference.

Let's see, the number of payment transactions grew to 4.4 billion, up 27%. This resulted in operating cash flow of $1.35 billion, up 46%, and free cash flow of $1.12 billion, up 50%.

It's really remarkable the amount of cash that they are reaping just quarter after quarter and year after year. I think that's one of the reasons that the market is really starting to recognize the opportunity in the digital payments sector. As a result of that, over the last little more than a year, companies like PayPal and like Square have been significantly bid up because of that growing digital payments opportunity.

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