In renewal, app purchase subscriptions do not work as expected

Question

I implemented an in-app purchase in my application.
The first time he requested confirmation of the authenticity of itunes and confirmation of purchase.
I keep receiving confirmation in NSUserDefaults.
After the expiration date (I test in the Sandbox, so 5 minutes), when I take the application, I check the receipt. Sometimes it returns status 21006, and sometimes 0. I could not understand why this is happening.
Will Apple automatically renew your subscription. If YES, then why does it return 21006 status several times. Should I do something else for the subscription function.
Please help me. I am really stuck with this.

Answer 1

I had a similar experience. I'm not sure what you know, but not only the durations reduced in the sandbox, but the extensions are limited to 5 times (I think). Therefore, if you check 25 minutes after the initial purchase (for example), the subscription must be expired. I found that the sandbox is thin and not quite consistent.