Reading coding the official website of them, you can see that typography is: Sans PP (PayPal Sans). That is, a font created by themselves.

Also, I got this extracted from: http://www.noupe.com/design/paypal-sans-the-new-exclusive-font-for-paypal.html

"Designed exclusively for PayPal by the Klim Type Foundry, PayPal Sans comprises of two sub-families: PayPal Sans Big and PayPal Sans Small, as well as 14 styles. As a custom font, PayPal Sans is something you will see in use exclusively on PayPal website and mobile apps."

https://klim.co.nz/blog/paypal-sans-design-information/