SoFi and dozens of other startups also use the credit card. : Brex, a fintech startup backed by PayPal cofounders Peter Thiel and Max Levchin, has raised $50 million in new venture capital, the company announced Tuesday. Y Combinator led the Series B funding round for San Francisco-based Brex, which participated in the tech accelerator’s winter 2017 class and now provides credit cards to many of its portfolio companies.