ShoppingCart.js

const ShoppingCart = () => {

  const [errorMessage, setErrorMessage] = useState(null)
  const isLoggedIn = useSelector((state) => state.account.isLoggedIn);
  
  const urlToUse = isLoggedIn ? 'https://api/customercheckout' : 'https://api/guestcheckout';
  
  const addToCartFunction = async (items) => {
    const { data, errors } = await axios.post(urlToUse, {items});
    if(errors){
      setErrorMessage('Oops, something went wrong...')
    }
  }
  
  return ...
}