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I am testing the auto renewable In-app purchases in swift, I found out that there are some strange problems with my code.

I am testing these functions in sandbox environment

1. User can purchase either one month, one year auto renewable subscription or permanent permission
2. App should check if the subscription is still valid every time when user open app, if not, lock all premium functions
3. User is able to restore the purchased plan, app should get the previous purchased type ie. one month, one year, or permanent.

After long research on the tutorials, I am still confused about the validation

1. I see that there are two ways to validate receipt, one is locally the other is on the server. But I don't have a server, does that mean I can only validate it locally
2. Every time the auto-renewal subscription expires, the local receipt is not updated, so when I reopen the app I got a subscription expiration alert (The method I defined by my self for validation check ), when I click the restore button, the app restored successfully and receipt was updated
3. After 6 times manually restored and refresh the receipt (the sandbox user can only renew 6 times), when I click the restore button, the part transaction == .purchased is till called, and my app unlocks premium function, however when I reopen my app, my app alerts that the subscription is expired, which is it should.

My core problem is how can I check the validation of subscriptions with Apple every time when I open the app, I don't have a server, and I don't know why the receipt is not refreshing automatically

Here are some parts of my code, I call checkUserSubsriptionStatus() when I open the app, I am using TPInAppReceipt Library