How can i do In-App purchase?
It would be much appreciated if you researched the topic before asking.
However, take a look at Google Play Services. Google's In-App billing is now a part of that: https://developer.android.com/google/play/billing/index.html
There is a component in the component store which you can use for Google Play Services.
Xamarin just released an official component that supports Google Play In-App Billing (API Version 3) in the component store. You can get a copy here, if interested: http://components.xamarin.com/view/xamarin.inappbilling
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