This Is How PayPal Uses AI/ML To Manage $712 Billion Payments

Primarily PayPal uses logistics regression for fraud detection.. 

For the tech stack, PayPal runs one of the most massive hybrid-cloud environments in the world. It hosts multiple technologies in each layer and function. Around 2700 applications are running over 20000 servers with 238 PetaBytes of storage.

https://analyticsindiamag.com/this-is-how-paypal-uses-ai-ml-to-manage-712-billion-payments/