I have developed an Win-Phone8 application, Initially for 15 days I am giving my application for trail period and after 15 days the user have to subscribe the application (They can purchase) to use it uninterruptedly rest of the time , I was planning to use third party payment gateways like (Stripe,Paypal) but I think the Platform like Windows only allowing third party payment gateways for selling physical goods like (Books , Electronics items etc. ) But in our case we just going to sell an upgraded App which is a digital content.My Question is can we sell the App Upgrade features through Stripe payment gateway or any third party payment gateway??? IF not I found the platform Windows providing Service API's for In-App Purchase inside the App. So My Question is, Do i need only In-App purchase service for selling App in Windowsstore???
Yes. In-app purchase given by Microsoft is enough for selling apps in windows store. You don't need to worry about third party payment gateway etc.
refer to this link https://msdn.microsoft.com/en-in/library/windows/apps/jj206949(v=vs.105).aspx
examples given on this page are useful.