CODE EXAMPLE FOR CSHARP

app rating within game in unity

using UnityEngine;
#if UNITY_IOS
using UnityEngine.iOS;
#endif

public class RateManager : MonoBehaviour
{
    public void RequestRateGame(){
#if UNITY_IOS
        Device.RequestStoreReview();   //displaying in app review widget
#endif
    }
}

/*
Note: this code works only for iOS
*/