Likely Adyen considering the press release that came out a couple years ago. But I wouldn't be surprised if they were also using Braintree at some point.

https://www.adyen.com/press-and-media/2019/postmates-selects...

It might be Adyen based off this press release.

https://www.adyen.com/press-and-media/2019/postmates-selects...