Does Microsoft supply an (non .NET) API to check for a previous in-app purchase that does NOT require using the network?

Question

I have an EXE application written using the Microsoft MFC application. It's installed using the Inno Setup installer.

I wish to add in-app purchase code. What I really want is a one-time fee for purchasing the application, however, since the Microsoft Store doesn't support that directly, I have to add code to my application.

I was pointed to both Stack Overflow and Github based on previous contacts with Microsoft support. I found code there, however, it does the purchase, and although it detects if a purchase already took place if the user tries to purchase an item twice, it doesn't have any function to determine if a purchase already took place. (I haven't tested any of the code yet - I have no idea if it works).

So that the user won't require an Internet connection after making a purchase, I will save secure encrypted data to ensure the purchase took place. It occurs to me that this might already be being done. Is this done, and I need to find the correct API to check for an existing purchase - or - must I write this code myself?