TS2322: Type 'IToken | undefined' is not assignable to type 'WritableDraft | null'

Question

Inside of Redux toolkit thunk I'm making axios call to server and recieve data of type IToken. I also created axiosClient and user function. Problem is with typescript. When I make axios call inside of thunk instead of putting it in seperate file all works as intendead. Other then that error code is operational. Axios Client I took from another perfactly working project with same functionality, and I wasn`t touching that code - so I couldnt broke it.

import { createSlice, createAsyncThunk } from '@reduxjs/toolkit';
import axios from 'axios'
import { signup } from '../../api/users';
import { IToken } from '../../types/IToken';
import { IRegister } from '../../types/IRegister';

type InitialState = {
  user: IToken | null;
  status:'idle' | 'failed' | 'pending' | 'fullfilled';
  error: string | null;
};

const initialState: InitialState = {
  user: null,
  status: 'idle',
  error: null,
};

export const registerUser = createAsyncThunk('user/registerUser', async (data: IRegister, thunkAPI) => {
  try {
    return await signup(data);
  } catch (err ) {
    if (axios.isAxiosError(err)) {
      if (
        err.response
        && err.response.data
        && err.response.data.error
      ) {
        return thunkAPI.rejectWithValue(err.response.data.error);
      } else {
        return thunkAPI.rejectWithValue(err.message);
      }
    }
  }
});


const userSlice = createSlice({
  name: 'user',
  initialState,
  reducers: {
    logOutUser: (state) => {
      state.user = null;
      state.error = null;
      state.status = 'idle';
    },
  },
  extraReducers(builder) {
    builder
      .addCase(registerUser.pending, (state) => {
        state.error = null;
        state.status = 'pending';
        state.user = null;
      })
      .addCase(registerUser.fulfilled, (state, action) => {
        state.status = 'fullfilled';
        state.error = null;
        state.user = action.payload;
      })
      .addCase(registerUser.rejected, (state, action ) => {
        if (typeof action.payload === 'string') {
          state.error = action.payload;
        }else {
          state.error = 'error';
        }
        state.status = 'failed';
        state.user = null;
      });
  },
});

export const { logOutUser } = userSlice.actions;

export default userSlice.reducer;

I have an error: here is axiosClient with function

import { client } from './axiosClient';
import { IRegister } from '../types/IRegister';
import { IToken } from '../types/IToken';

export const signup = (post: IRegister) => {
  return client.post<IToken>('/user/signup', post);
};

import axios from 'axios';

const instance = axios.create({
  baseURL: 'http://localhost:8000/api',
  headers: {
    Accept: `application/json`,
  },
});

export const client = {
  async get<T>(url: string) {
    const response = await instance.get<T>(url);

    return response.data;
  },

  async post<T>(url: string, data: any) {
    console.log(url, data);
    const response = await instance.post<T>(url, data);
    return response.data;
  },

  async patch<T>(url: string, data: any) {
    const response = await instance.patch<T>(url, data);

    return response.data;
  },

  async delete(url: string) {
    return instance.delete(url);
  },
};