Integrate jQuery

Hi there, I’ve been trying for hours and simply can’t get this to work. My jquery works perfect on Codenpen but nothing on WordPress.

My code is:

add_action( 'wp_enqueue_script', function () {
	wp_enqueue_script( 'jquery' );
});

?>

<script>

	function runFunction(){
$.noConflict();
jQuery(document).ready(function(){
    // Your code in here
  jQuery('#billing_test').on('change', function() {
  myFunc();
})
function myFunc() {
    // your function code
var complex_name = jQuery('#billing_test').val();

var suburb = jQuery('#billing_suburb').val();

if (complex_name == 'mr') {
 alert('works');
   
   jQuery('#billing_postcode').val('5000');
   
  
}
 }
})
							   
	}

</script>

<?php

add_action( 'wp_head', 'runFunction');

I’ve tried with both $ and jQuery, it runs perfect in CodePen using the same code with corresponding HTML but does nothing on WP.