Redux Thunk, Modifying state: Unhandled promise rejection: Error: [Immer] Immer only supports setting array indices and the 'length' property]

While working on a React Native application with a persistent Redux store (in TypeScript) I ran into the following problem:

I built a Thunk that queries an API, this API sends back a set of question data in a fetch. This fetch works fine, but when trying to save any data to the Redux Store using extraReducers I get errors.

My code looks like this:

First I call a dispatch on the Thunk in my page:

questionpage.tsx-stuff-    useEffect(() => {        console.log('dispatching fetch')        dispatch(fetchQuestions())    }, []);-render stuff-

The actual thunk looks like this and does a fetch to my API:

export const fetchQuestions = createAsyncThunk('questions/fetchquestions', async () =>{    let headers = new Headers();    headers.append('Authorization', 'Basic '+ Base64.btoa(email +":" + password))    const response = await fetch(api +"/api/questions", {            headers: headers,            method: 'GET'        })    const stuff = await response.json();    console.log(stuff)    return stuff;})

Then:

questionSlice    extraReducers: (builder) => {        builder.addCase(fetchQuestions.pending, (state, action) => {          state.status = 'loading' // < when I comment this the console.log works          console.log('pending')        }),        builder.addCase(fetchQuestions.fulfilled, (state, action) => {          state.status = 'succeeded'          // Add any fetched posts to the array          state.questions = state.questions.concat(action.payload) // < comment this, console.log works          console.log('fulfilled')        })        builder.addCase(fetchQuestions.rejected, (state, action) => {          state.status = 'failed' // < when I comment this the console.log works          state.error = action.error.message // < when I comment this the console.log works          console.log('rejected')        })      } 

As you see above: In my reducer I use the extraReducers to catch the different results this Thunk can produce. This works, but only when I modify nothing in the state. If I try to save anything to the state I get the following error:

[Unhandled promise rejection: Error: [Immer] Immer only supports setting array indices and the 'length' property]

This error occurs at all times, it occurs when I modify state.status, which is a String, not an Array, it also occurs when I modify state.error and state.questionsThe last one is an array, but the other two are not.

I looked at a lot of other questions but couldn't find this specific scenario anywhere and am fairly lost on how to proceed.

Update:My problem stems from Immer. If I understand the documentation correctly Immer should allow me to do updates of objects in the Redux state, but I cannot get it to work:

export const questionSlice = createSlice({    name: 'question',    initialState,    reducers: {         save: (state, action) => {            state.questions.push(action.payload) < this action works        }    },    extraReducers: (builder) => {        builder.addCase(fetchQuestions.fulfilled, (state, action) => {          state.questions.push(action.payload) < this action errors        })