Почему асинхронный запрос не выполняется?

const mapStateToProps = state => {
  return {
    items: state.items.items,
    error: state.items.error,
    loading: state.items.loading
  };
};

export function items(state = initialState, action) {
  const { type, payload } = action;

  switch (type) {

    // some code

    case "FETCH_SUCCESS":
      return { 
        ...state,
        items: [ ...state.items, ...payload.items ],
        loading: false,
      };

     // some code

  }
}

export const fetchProductsBegin = () => ({ type: FETCH_BEGIN });

const mapStateToProps = state => ({
  items: state.items.items,
  error: state.items.error,
  loading: state.items.loading,
});