You could create a new in-app purchase that unlocks the same feature and set the price to FREE. If the user provides the code before unlocking, use this new in-app identifier ID.

This will only query live apps but you can use iTunes Search API ( https://developer.apple.com/library/archive/documentation/AudioVideo/Conceptual/iTuneSearchAPI/Searching.html#//apple_ref/doc/uid/TP40017632-CH5-SW1 ). The response includes "currentVersionReleaseDate" and "releaseDate"

When you say "it doesn't work", what error are you seeing?

Not directly. You will need to use a responsive/adaptive layout.

No, this is not offered out of the box. You need to create it for yourself: keep track of transactions then register for server updates to know when a subscription expires. You can also verify receipts to get the real-time status.

"But Apple isn't responding." what error are you getting, timeout?

Unfortunately, there is no direct way to query for such a thing. However, some workarounds have been sued in the past. None are perfect. Some to consider: request location and if altitude value is present you have gps. match useragent/device model against a table of known devices with GPS (will need to be maintained) check connection (if on cellular, it will have GPS)

Test without using the local network and see the error returned.

I noticed when a country code is missing the device adds the default country code for the device in use. If the provided phone number does not include it, make sure to request it.

Can you replicate the vetting process within the app? What do you mean by "a log of all the IDs of users"... emails? transaction ID? device ID? You will only get transaction IDs. If you want an email or something identifiable you will need to ask the user to register in some way.

If the app can be a simple website, it has no reason to be a native app.