Custom Sign Message from Unity to metamask

hey Developer i have integrated Moralis SDK in my Game.
all going well. but I have a question, I need to send my own (Custom)sign msg rather than moralis,
like Moralis one is :
string signMessage = $“Moralis Authentication\n\nId: {ServerNounce}:{serverTime}”;

this message is sent to metamask for sign-in and we get a response after that Moralis authenticated it and Logged in.

now my question is I want to send and sign my own custom msg for example (msg may be “XYZ”).

so when I send XYZ to metamask wallet for signing, there in metamask wallet it gives me pop up and signed the msg,
now on game Side, i get the response from Metamask which is a signed message, now it has an issue, it doesn’t allow me to log in to metamask and give.
giving error in :

"USer services extension class "
public static Task LogInWithAsync(this IServiceHub serviceHub, string authType, IDictionary<string, object> data, CancellationToken cancellationToken) where TUser : MoralisUser
TUser user = null;

        return serviceHub.UserService.LogInAsync(authType, data, serviceHub, cancellationToken).OnSuccess(task =>

            user = task.Result;
            Debug.Log(task.Result);      // the task.result give me null.

need help related to it.
please respond quickly

[email protected]