Dear Sir,
I'm Nicky, I believe your needed application can be built using C# .NET. I have worked with interfacing many APIs such as Payment Gateway, Facebook, Twitter, LinkedIn ...
There is no difficulty with technicality here, I believe. Major point here is that you want a freelancer who has good experience. So please visit my profile page on freelancer.com you will see my results.
I have worked with .NET for 6 years and now I'm technical project manager for largest software company in Viet Nam. With my experience, I will satisfy you, trust me!
Thanks,
Nicky