how to sign a user for the game

I am a beginner game developer. Tell me how to organize the possibility of a user subscribing to the game (on the user side, on the server side), how to track the subscription period (I set the necessary IDs in the IAP catalog). I can’t figure out how to use the toolkit described in https://docs.unity3d.com/en/current/Manual/UnityIAPSubscriptionProducts.html,

I managed to solve this problem. Detailed instructions - in the article: