Нужно переписать extraReducers под новый формат:
extraReducers: (builder) => {
builder
.addCase(registerUser.pending, (state) => {
state.isLoading = true;
state.status = null;
})
.addCase(registerUser.fulfilled, (state, action) => {
state.isLoading = false;
state.status = action.payload.message;
state.user = action.payload.newUser;
state.token = action.payload.token;
})
.addCase(registerUser.rejected, (state, action) => {
state.isLoading = false;
state.status = action.payload.message;
});
},
Типо так )