The problem is that few card processors will underwrite you for your small transaction volume at the start, so PayPal/Braintree and Stripe are go-to solutions w

The problem is that few card processors will underwrite you for your small transaction volume at the start, so PayPal/Braintree and Stripe are go-to solutions with the promise to scale up without ever needing to rewrite your payment processing code. Once you get big, you can either seek out a real contract with the services (but this requires a lot of scale) or go for something like Adyen or Chase which seem to still require some level of scale but not a million dollars a day or anything.