Return error content to client from ASP.NET Core using hot chocolate

Question

I'm using Hot chocolate in ASP.NET Core. If userExist != null is true, I return the GraphQLException to the client to process and display to the user (I'm using Angular and apollo client). But I can't catch the return error and get internal server error in the console screen.

Below is my mutation.

public async Task<UserType?> CreateUser([UseFluentValidation, UseValidator<RegisterInputTypeValidator>()]RegisterInputType model, [Service]IUserRepository userRepository)
{
    var userExist = await userRepository.GetUserByEmail(model.Email);

    if (userExist != null)
    {
        throw new GraphQLException(new List<Error>()
        {
            new Error("Email already exists"),
        });
    }

    AppUser user = new AppUser
    {
        Email = model.Email,
        FullName = model.FullName,
        UserName = model.Email,
        AvatarUrl = model.AvatarUrl,
        PhoneNumber = ""
    };

    var r = await userRepository.CreateUserAsync(user, model.Password);

    if (r.Succeeded == false)
    {
        var err = r.Errors.Select(e => new Error(e.Description)).ToList();
        throw new GraphQLException(err);
    }

    return new UserType
    {
        Email = user.Email,
        FullName = user.FullName,
        AvatarUrl = user.AvatarUrl,
        PhoneNumber = user.PhoneNumber!,
        FriendIds = user.FriendIds,
        GroupIds = user.GroupIds
    };
}

This is my Angular code:

this.apollo
    .mutate({
        mutation: CREATE_USER,
        variables: {
            email: this.registerForm.controls['email'].value,
            fullName: this.registerForm.controls['fullName'].value,
            password: this.registerForm.controls['password'].value,
            reEnterPassword: this.registerForm.controls['reEnterPassword'].value,
            avatarUrl: '',      
        },
    })
    .subscribe({
        next: (result) => {
            console.log(result);
        },
        error: (err) => {
            // not working
            console.log(err.message);
        }
    });

I tried everything and nothing worked. How to return the errors to the client?