I am offering a subscription to users right when they sign up to my iOS app. If the user does not purchase the subscription offer at sign up, I want to give them the premium version of the app for 7 days. Once the 7 days past I want the user to have to purchase a subscription to continue to use the app.
I do not want to do just a basic counter/timer in the app because users' can just delete and reinstall the app to get full access once their time is up.
What is a possible way of accomplishing this?
Apple provides a way to do that. but it supports iOS 11.0+ It's called DeviceCheck
From the docs:
Access per-device, per-developer data that your associated server can use in its business logic.
You can set two bits data per device and keep in mind that it is dev's responsibility for keeping track of whether a user is entitled to redeem any offer that you provide.
A good way to start