Easiest way to create an online userbase

I wasn't sure how to word this, so hopefully I get the point across alright. Basically, I am planning on releasing this program, and I want it to be a subscription based payment. So I want to force everyone to login, and I want to be able to control the accounts in the database that it is checking so that I can remove an account if their subscription is over and they haven't paid. This program was done in Visual Studio using Windows Forms and obviously c#. I've tossed around a ton of ways to do this in my head, but I really can't think of the best / easiest way. There won't be a massive number of users. I've thought about using googles api to use sheets or download a file from drive every time, but I don't think that either of those would work as they would have to be signed into my google account? Hopefully someone has a good idea for this. Thanks.

Hi Chase Meade,

I think you can implement it like this, at the point of payment set the subscription date and save it into the database and also calculate the expiry date and save it also to a column in the database.

So your table would have SubscriptionDate and expiry date.

Then also create another column called payment status, it can be string then you can set the payment status to active if the expiry date is greater than today's date. else if today's date is greater than the expiry date, then set the payment status to expired. But make sure you write a function that is called(this function should check the subscription if it's still active) whenever the user requests a resource. if the payment status is active then display the resource else don't display the resource.