App Branching with Google Analytics 4: Got an exception while running a Xamarin Forms Android app

I am a Xamarin developer and I have followed the URL https://help.branch.io/partners-portal/docs/google-analytics-4#properties-sent-to-google-analytics to integrate Google Analytics 4 in Xamarin forms Android to send branch data to Google Analytics dashboard, but I got exception while running the app, saying

> BranchXamarinSDK.BranchException: you must initialize Branch before you can use the Branch object

I have implemented code below in MainActivity.cs

protected override void OnCreate(Bundle savedInstanceState) 
{ 

base.OnCreate(savedInstanceState); 

// Set the request metadata before initializing the Branch SDK 
BranchAndroid.GetInstance().SetRequestMetadata("$firebase_app_instance_id", (string) FirebaseAnalytics.GetInstance(this).GetAppInstanceId()); 
BranchAndroid.GetInstance().SetRequestMetadata("$firebase_user_id", "{user_id}"); 

BranchAndroid.Init(this, Resources.GetString(Resource.String.branch_test_key), this); 

LoadApplication(new App()); 

} 

No, if you want to call the SetRequestMetadata() method, the BranchAndroid.GetInstance() must have value or it will be null.

In addition, I have check the official document about the Branch and the resource code about the BranchAndroid.

The official document said:

So just make the SetRequestMetadata() called before the session initialization and after the instance initialization is ok. Your code should be:

protected override void OnCreate(Bundle savedInstanceState) 
{ 

base.OnCreate(savedInstanceState); 

BranchAndroid.Init(this, Resources.GetString(Resource.String.branch_test_key), this); 
// Set the request metadata before initializing the Session 
BranchAndroid.GetInstance().SetRequestMetadata("$firebase_app_instance_id", (string) FirebaseAnalytics.GetInstance(this).GetAppInstanceId()); 
BranchAndroid.GetInstance().SetRequestMetadata("$firebase_user_id", "{user_id}"); 
LoadApplication(new App()); 

}