Toggle checkbox

toggle-checkbox.php

<?php

add_action( 'wp_head', function () {
	if($post->ID == $pmpro_pages['checkout'])
  {
?>
	<script>

		/* JavaScript code here */
		window.onload = function() {
		document.getElementById("additional_lists_1").checked = true;
		}
	</script>
<?php } } );