Cannot read property 'user' of undefined, React Redux - reactjs

Question

I have been getting this error "Cannot read property 'user' of undefined" in a userSlice.js which by default is named as counterSlice.js in react-redux. I have tried exporting by changing names and function names too, and I guess I am exporting the right function.
any suggestions or fix that might get it running?
Here is my userSlice.js file,
import { createSlice } from '#reduxjs/toolkit';
export const userSlice = createSlice({
name: 'user',
initialState: {
user: null,
},
reducers: {
login: (state, action) => {
state.user = action.payload;
},
logout: (state) => {
state.user = null;
},
},
});
export const { login, logout} = userSlice.actions;
export const selectUser = state => state.user.user;
export default userSlice.reducer;
here is the store.js file,
import { configureStore } from '#reduxjs/toolkit';
import userReducer from '../features/userSlice';
export default configureStore({
reducer: {
counter: userReducer,
},
});
and here is the App.js file where I am trying to make the login user state to be logged in,
import React, {useEffect} from 'react';
import './App.css';
import Homescreen from "./screens/Homescreen";
import LoginScreen from "./screens/LoginScreen";
import {auth} from "./firebase";
import {useDispatch, useSelector} from "react-redux";
import {login, logout, selectUser} from "./features/userSlice";
import {BrowserRouter as Router, Switch,Route} from 'react-router-dom';
function App() {
const user = useSelector(selectUser);
const dispatch = useDispatch();
useEffect(() => {
const unsubscribe = auth.onAuthStateChanged((userAuth) => {
if(userAuth){
dispatch(login({
uid: userAuth.uid,
email: userAuth.email,
})
);
} else{
dispatch(logout())
}
});
return unsubscribe;
}, []);
return (
<div className="App">
<Router>
{!user ? (
<LoginScreen/>
):(
<Switch>
<Route exact path="/">
<Homescreen />
</Route>
</Switch>
)}
</Router>
</div>
);
}
export default App;

Answer 1

The problem is here
export const selectUser = state => state.user.user;
You created slice with name counter here
export default configureStore({
reducer: {
counter: userReducer,
},
});
Try
export const selectUser = state => state.counter.user;
Or rename counter to user