Next.js with typescript - useContext error

I'm developing an app, for the fronted i'm using next.js, and i had problem trying to stringify an object, this is how the error looks like

Argument of type '{ auth: dataObject; }' is not assignable to parameter of type 'string'

So what happens is that when a user log in i'm trying to save some data localStorage, and as far as i know, if you save data there it must be as a tring ( i really don't know why ) so that's why i'm using json.stringify ( in my code ).

Now, to give you more context, let me show you my code

This is my context - useReducer part ( the problem is in LOGIN case ! )

import { createContext } from "react";

import {
  Actions,
  dataObject,
  LOGIN,
  LOGOUT,
  LOADING
} from "../GlobalInterfaces/AuthContextInterfaces";
import { useReducer } from "react";
import { useContext } from "react";

interface Istate {
  loading: boolean;
  data?: dataObject | null;
}

const DefaultState = createContext<Istate>({ loading: false });

const DispatchActions = createContext(null);

const localReducer = (state: Istate, action: Actions): Istate => {
  switch (action.type) {
    case LOADING:
      return {
        ...state,
        loading: true
      };

    case LOGIN:
      JSON.stringify(localStorage.setItem("Auth", { auth: action.payload }));
      return {
        ...state,
        loading: false,
        data: action.payload
      };

    case LOGOUT:
      localStorage.removeItem("Auth");
      return {
        ...state,
        data: null
      };

    default:
      return state;
  }
};

export const AuthContext = ({ children }: { children: React.ReactNode }) => {
  const [state, dispatch] = useReducer(localReducer, {
    loading: false,
    data: null
  });

  return (
    <DefaultState.Provider value={state}>
      <DispatchActions.Provider value={dispatch}>
        {children}
      </DispatchActions.Provider>
    </DefaultState.Provider>
  );
};

export const AuthData = () => useContext(DefaultState);
export const AuthActions = () => useContext(DispatchActions);

And these are my types and interfaces that i'm using with useContext and useReducer

// Data

export type dataObject = {
  token: string;
  user: { id: string; email: string; name: string };
};

// Options's Actions

export const LOGIN = "LOGIN";
export const LOGOUT = "LOGOUT";
export const LOADING = "LOADING";

interface IloginAuth {
  type: typeof LOGIN;
  payload: dataObject;
}

interface IloginLogout {
  type: typeof LOGOUT;
}

interface Iloading {
  type: typeof LOADING;
}

export type Actions = IloginAuth | IloginLogout | Iloading;

SO what can i do to fix my code ? can i skip the JSON.stringify ?

Thanks for your time !