I'm having the exact same issue. When I have this code at the top of one of my JS files:

import AgoraRTC from "agora-rtc-sdk-ng";

...I get the same error as the original poster. Any ideas?

I made a combineSlices helper function to make it easy to adapt @agrinko's suggestion to any use case (note that it requires that you install reduce-reducers):

import { combineReducers } from "@reduxjs/toolkit";
import reduceReducers from "reduce-reducers";

/**
 * Combines a slice with any number of child slices.
 *
 * This solution is inspired by [this GitHub
 * comment](https://github.com/reduxjs/redux-toolkit/issues/259#issuecomment-604496169).
 *
 * @param sliceReducer - The reducer of the parent slice. For example, if your
 * slice is called `mySlice`, you should pass in `mySlice.reducer`.
 * @param {object} sliceInitialState - The initial state object passed to
 * `createSlice`. This is needed so that we know what keys are in the initial
 * state.
 * @param {object} childSliceReducers - An object of child slice reducers, keyed
 * by the name you want them to have in the Redux state namespace. For example,
 * if you've imported child slices called `mySlice2` and `mySlice3`, you should
 * pass in this argument as `{ mySlice2: mySlice2.reducer, mySlice3:
 * myslice3.reducer }`.
 */
const combineSlices = (sliceReducer, sliceInitialState, childSliceReducers) => {
  const noopReducersFromInitialState = Object.keys(sliceInitialState).reduce(
    (prev, curr) => {
      return {
        ...prev,
        [curr]: (s = null) => s,
      };
    },
    {}
  );

  const childReducers = combineReducers({
    ...childSliceReducers,
    ...noopReducersFromInitialState,
  });

  return reduceReducers(sliceReducer, childReducers);
};

export default combineSlices;

Note that you need to pass it the initial state from the parent slice so that it knows what keys to make dummy no-op reducers for. Thus, here's an example of how it could be used:

import mySlice2 from "./mySlice2"
import mySlice3 from "./mySlice3"
import combineSlices from "./combineSlices"

const initialState = {
  count: 0,
}

const mySlice = createSlice({
  name: "mySlice",
  initialState,
  reducers: {
    setCount(state, action) {
      state.count = action.payload
    },
  }
})

export default combineSlices(mySlice.reducer, initialState, {
  mySlice2: mySlice2.reducer,
  mySlice3: mySlice3.reducer,
})