How to payment gateway Xamarin Android Using Sprite

They have provided a working sample on the documentation page, that is why I gave it to you. Have a look at their work flow, the work flow of any payment gateway is simple:

1. Enter the credentials.
2. Chose how much to pay.
3. Done.

Every provider will have their own documentation of, "how to do that", and that is what I provided you there. :-)  

Do you mean to say Stripe? Xamarin has the feature as a component, that you can use in your applications. Please see here, https://components.xamarin.com/view/stripe.