We have got a problem with auto renewable subscription. First, I would like to tell you my case from the beginning to understand my problem totally.
So, I have an app that contains auto renewable subscription. I managed to buy a product from my app, but I would like to validate the receipt from my server. If I understand it well, then I should send the receipt data to my server that will send the receipt data to Apple and verify that receipt.
First question is that, do I know it right that verification means that we send a request to https://sandbox.itunes.apple.com/verifyReceipt ?
Secondly, what happens if I cannot send the receipt data for the server? I mean, in this case should I save the receipt data locally and try to send it again in a different time (my app can be used after registration so I have to send the user id with receipt data to my server)?
Furthermore, there is a subscription status URL for auto renewable subscription in iTunes connect. We set up an URL for this but we do not get any notification from Apple's server. We configured the server as explained in Apple's documentation (protocols, etc.) but we still don't get any notification. Do you have any suggestion why is it?
Do I know it well, that the notifications should be sent automatically if any status update change happens? If not then what should I do in my app or on my server? (e.g. how to detect if user cancels a subscription?)
Do I have to implement both logic for the best user experience?
To validate the receipt you can send it on apple servers, "can" because you can validate the receipt also in app. In this case is not fully safe, because someone can attack you app and tamper your validation code.
Apple has 2 different kind of servers test and production, when you are debugging you send receipt to the test servers, that also means that auto renewable subscription have shorter time, if I remember well a month in test is 5 minutes.
This is documented very well in apple documentation.
A receipt is always present in your app even if it's free. It's up to you how to manage those kind of situation, in my opinion a receipt should aways be valid from the beginning until the server responds in a different way.
The third question is not clear. There is a system to refresh a subscription but this should be done with user permission as far as I know, the subscription itself seems to be already updated automatically from time to time by the purchase mechanism.
You must implement all the logic to manage a subscription, cancellation, revocation etc.