How do I implement In-App purchases for Windows/Windows Phone?

Is it necessary to buy a plugin? If so, is there a specific one for Windows, or do they work the same for any platform? Is there anything additional that I would need to do when submitting to Microsoft?

I haven’t tried anything yet, as I have no idea how where to start and there is no information regarding this online. I am completely new to app development and IAP. Thanks.

IAP is a very important part of the project. They are platform specific, but can be realised in one plugin and work the same on every platform, but different in their native part. if you write a plugin by yourself you could add own protection from hacks. I think IAPs is not a part that you should relay on third-parties, i wrote it myself. If you do the same you’ll better understand a specific of purchase processing and be able to more rightly solve an issues with your users.
You should start with in app purchases for windows store apps. And when you implement it in a native windows app, you can transfer your code to Unity Plugin for Windows.

You can start with Soomla it is free plugin, easy to implement and supports IOS, Android and Windows store.