I saw that a some people encountered this issue but none of the answers help me actually.

So, I'm creating an app on unity (2020.1.11f1) and I'm using Firebase to deal with the authentication process. Email/Password authentication is working but now that I'm dealing with facebook authentication, I'm running into the famous error:

Firebase.FirebaseException: The supplied auth credential is malformed or has expired

I logged my app into facebook developper and connect it to firebase. I doubled check App ID and Secret ID. Also, my token is valid since I'm checking its validity. Also, it knows that it is coming from facebook.

I'm using the piece of code (coming from official documentation):

private void facebook_loginFirebase(string accessToken)
        {
            //Get firebase authenticator and credential to perform connection
            Firebase.Auth.FirebaseAuth auth = Firebase.Auth.FirebaseAuth.DefaultInstance;
            Firebase.Auth.Credential credential = Firebase.Auth.FacebookAuthProvider.GetCredential(accessToken);

            //Perform Connection
            auth.SignInWithCredentialAsync(credential).ContinueWith(task => {
                if (task.IsCanceled)
                {
                    Debug.LogError("SignInWithCredentialAsync was canceled.");
                    popup_manager.openErrorPopup("5010", "Task has been cancelled");
                    return;
                }
                if (task.IsFaulted)
                {
                    Debug.LogError("SignInWithCredentialAsync encountered an error: " + task.Exception);
                    popup_manager.openErrorPopup("5011", "An error happened: " + task.Exception);
                    return;
                }

                Firebase.Auth.FirebaseUser newUser = task.Result;
                Debug.LogFormat("User signed in successfully: {0} ({1})",
                    newUser.DisplayName, newUser.UserId);
                popup_manager.openInformationPopup("Account created with userID: " + newUser.UserId);

            });
        }

Also, I'm using Facebook SDK 9.0. It seems it has changed a bit from previous versions and all tutorial on internet are based on old versions. Do you have any more tips to check?

Thanks in advance! Let me know if I need to give you more information!