Unity google-play-core review issue - unity3d

Question

I added the google play core package as instructed in the repo, and added the code according to the documentation here
I receive the following error: CS0246: The type or namespace name 'PlayAsyncOperation<,>' could not be found (are you missing a using directive or an assembly reference?)
This error shows at _reviewManager.RequestReviewFlow(); and _reviewManager.LaunchReviewFlow(_playReviewInfo)
Any idea what could be the issue?
My full code:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Google.Play.Review;
public class ReviewCodes : MonoBehaviour
{
private ReviewManager _reviewManager;
private PlayReviewInfo _playReviewInfo;
// Start is called before the first frame update
void Start()
{
StartCoroutine(RequestReviews());
}
// Update is called once per frame
void Update()
{
}
IEnumerator RequestReviews()
{
// Create instance of ReviewManager
_reviewManager = new ReviewManager();
var requestFlowOperation = _reviewManager.RequestReviewFlow();
yield return requestFlowOperation;
if (requestFlowOperation.Error != ReviewErrorCode.NoError)
{
// Log error. For example, using requestFlowOperation.Error.ToString().
yield break;
}
_playReviewInfo = requestFlowOperation.GetResult();
var launchFlowOperation = _reviewManager.LaunchReviewFlow(_playReviewInfo);
yield return launchFlowOperation;
_playReviewInfo = null; // Reset the object
if (launchFlowOperation.Error != ReviewErrorCode.NoError)
{
// Log error. For example, using requestFlowOperation.Error.ToString().
yield break;
}
// The flow has finished. The API does not indicate whether the user
// reviewed or not, or even whether the review dialog was shown. Thus, no
// matter the result, we continue our app flow.
}
}

Answer 1

"are you missing a using directive or an assembly reference?"
These are following situation which causes a compiler error:
Check if the name of the type or namespace is correct, as most of the time you can get this error when the compiler cannot find that namespace.
Check if you have added the reference to the assembly that contains the namespace. Ex: Your code can be in "using XYZ;"
but if your project does not reference assembly then you can get a CS0246 error.
Try: using Google.Play.Common;

Answer 2

the order might be your problem. You also not only have to import the Google Core Package. You also have to import the Google Review Plugin. The core plugin overrides assemblies and files which then can't be used by the review assembly.
Step-by-Step solution:
Import google-play-plugins-1.7.0.unitypackage
Import com.google.play.review-1.7.0.unitypackage
Make sure to restart your IDE or reload the code in your IDE after this steps.
In older versions in unity there was an option to download this packages with the help of the unity package manager. Now you have to use the official github repository from Google. See Downloading the plugins or just use the official provided .unitypackages from Google