To solve this error i fixed store.js.
import { configureStore } from "@reduxjs/toolkit";
import userReducer from "./user/userSlice";
export const store = configureStore({
reducer: { user: userReducer },
middleware: (getDefaultMiddleware) =>
getDefaultMiddleware({
serializableCheck: false,
}),
});
//it was reducer: {userReducer}, so i added user:userReducer