Humbly recommend Lab Zero, particularly if you're looking for a team that combines product, design (all aspects) and development. We've designed and/or built payments apps for companies like Xoom, FiveStar, FHLB, PayPal, Payfone, Stockpile and a couple big ones we can't mention here. Here's a little more detail: https://labzero.com/landing/payments. read more