I’ve been trying out the same code snippet from Cloudways as well. If you don’t use the snippet in functions.php, but instead create a copy of the woocommerce file form-login.php in your child theme’s folder/woocommerce/myaccount. Then the fields from the Couldways snippet can be used before the line containing:
<?php do_action( 'woocommerce_after_checkout_billing_form', $checkout ); ?>