https://techcrunch.com/2019/06/21/google-pay-expands-its-integration-with-paypal-to-online-merchants/

Google and PayPal have been strategic partners for some time. The companies in 2017 announced that PayPal would become a payment method in Android Pay, the service that later rebranded as Google Pay. Last year, users who added PayPal as a payment method on Google Pay could then pay for services like Gmail, YouTube, Google Play, and Google Store purchases via a PayPal option in Google Pay. Now, a similar integration is making its way to online merchants who accept Google Pay on their website or mobile app.

Explains Google, hundreds of millions of customers already have payment methods saved to their Google Account — including in some cases, PayPal, thanks to the 2018 integration.