Yes, I have seen it. I do it exactly the way described in the apple's answer: I use a clear macbook (with no previus version of my app ever installed), and a new just created sandbox test user. Still no trial.
Actually, I'm confused with this link (https://developer.apple.com/documentation/storekit/in-app_purchase/implementing_subscription_offers_in_your_app?language=objc). As it says one has to implement SKPaymentDiscount signing and specify it in the SKPayment request. This article is about subscription offsers, not a word about trials. But in apple's terms, free trial is a kind of introductory offer (same as subscription offer?), so does the article apply to trials as well?
On the other hand, this link (https://developer.apple.com/documentation/storekit/in-app_purchase/implementing_introductory_offers_in_your_app?language=objc) is explicitly about free trials, and it says nothing about SKPaymentDiscount signing. According to it, it is enoughf to configure introductory offer in itunes connect and then app store manages trials by itself, it that true?
What I am asking is whether I have to implement SKPaymentDiscount signing in my app in order to get free trial to work, or it is enoughf to just configure introductory offer in itunes connect?
Thanks for answers, finally got this working in both production (app store) and sandbox environments.
No additional code is required on the client side, was my fault in itunes configuration (wrong date).