Hello,
Sorry guys, I don't understand if you are looking for a designer or a developer.
I'm UX/UI Designer, and I already designed a payment App called SwaPay (you can find it on Android and iOS platform). If you are looking for an Interface designer I can help you.
If you are looking for a developer I can also find one to create a team, I've lots of iOS and Android developer contacts that can be interested on doing a payment app.
Please, let me know if this is what you are looking for,
Thanks for reading
Julia