I’m using AppCheck version 12.1.0 for my Unity(version 2022.3.20f1)’s game with secondary firebase app instance follow this instruction https://firebase.google.com/docs/projects/multiprojects#use_multiple_projects_in_your_application. I also done setup app check in both my main and secondary firebase project via firebase console. Then, when I call appCheck.GetAppCheckTokenAsync for secondary firebase app, I get an exception One or more errors occurred. (Provider returned an Exception: System.AggregateException: One or more errors occurred. (Cannot parse null string) ---> Firebase.FirebaseException: Cannot parse null string. Follow is the simple code flow to demonstrate the firebase code flow in my project and full stacked trace for exception:

FirebaseAppCheck.SetAppCheckProviderFactory(PlayIntegrityProviderFactory.Instance);
FirebaseApp.Create(_appOptionsStagingAndroid, "SecondaryApp");
var instance = Firebase.FirebaseApp.GetInstance("SecondaryApp");
var appCheck = FirebaseAppCheck.GetInstance(instance);
var appCheckToken = await appCheck.GetAppCheckTokenAsync(false);

One or more errors occurred. (Provider returned an Exception: System.AggregateException: One or more errors occurred. (Cannot parse null string) ---> Firebase.FirebaseException: Cannot parse null string
08-02 15:23:05.567 31914 31984 E Unity   :    --- End of inner exception stack trace ---
08-02 15:23:05.567 31914 31984 E Unity   : ---> (Inner Exception #0) Firebase.FirebaseException: Cannot parse null string<---
08-02 15:23:05.567 31914 31984 E Unity   : )
08-02 15:23:05.567 31914 31984 E Unity   :   at Firebase.AppCheck.FirebaseAppCheck+<>c.<GetAppCheckTokenAsync>b__13_0 (System.Threading.Tasks.Task`1[TResult] task) [0x00000] in <00000000000000000000000000000000>:0
08-02 15:23:05.567 31914 31984 E Unity   :   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2[TAntecedentResult,TResult].InnerInvoke () [0x00000] in <00000000000000000000000000000000>:0
08-02 15:23:05.567 31914 31984 E Unity   :   at System.Threading.Tasks.Task.Execute () [0x00000] in <00000000000000000000000000000000>:0
08-02 15:23:05.567 31914 31984 E Unity   :   at System.Threading.ExecutionContext.RunInternal (System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSync

I have tried checking null and try catch for each step but the error always happened at appCheck.GetAppCheckTokenAsync. When I tried using FirebaseAppCheck.DefaultInstance instead of FirebaseAppCheck.GetInstance(secondaryFirebaseApp), I successfully got the app check token. Did I do anything wrong or any step that I’m missing? And what is the exactly exception ” Cannot parse null string” meaning? I just curious because I log all apiKey, appId and projectId for secondary firebase app instance and none of that is null or empty.