how to develop a online mobile recharge application in android?

I want to develop a online mobile recharge application in android, I am searching in the Google and find that some organizations provide api's (like easyliferecharge api, mayur recharge api... ) for online mobile recharge and dth recharge. But my problem was how to handle payment gateway for each transaction?I was not sure that I was in right direction.

So, please give an idea to how ca n i do that, and which resources are needed to develop a online recharge application in android?