2 demos to demonstrate the PMPro checkout_levels API call.

checkout_levels_api_demo.php

<?php

// Copy from below here...

/*
 * Add widget to checkout to get result of checkout_levels API call when button is pressed.
 */
function my_pmpro_test_checkout_levels_api() {
	?>
		<hr/>
		<textarea rows="6" id="my_pmpro_checkout_level_api_output" value=""></textarea><br>
		<button id='my_pmpro_test_checkout_level_api' type="button">Test API</button>
		<script>
		function my_pmpro_test_checkout_level_api() {
			jQuery.noConflict().ajax({
			url: '<?php echo( get_rest_url() ); ?>pmpro/v1/checkout_levels',
			dataType: 'json',
			data: jQuery( "#pmpro_form" ).serialize(),
			success: function(data) {
				jQuery('#my_pmpro_checkout_level_api_output').val( JSON.stringify( data ) );
			}
			});
		}

		jQuery(document).ready(function () {
			jQuery('#my_pmpro_test_checkout_level_api').click(function () {
				my_pmpro_test_checkout_level_api();
			});
		});
		</script>
	<?php
}
add_action( 'pmpro_checkout_before_submit_button', 'my_pmpro_test_checkout_levels_api' );

/*
 * Show live price above payment information box at checkout.
 * Note, this will make an API call after every field change at checkout
 */
function my_pmpro_live_price( $param ) {
	?>
		<h4 id='pmpro_live_price'>Total: $x.xx</h4>
		<script>
		jQuery(document).ready(function () {
			function pmproUpdateLivePrice() {
				setTimeout(function(){
					jQuery.noConflict().ajax({
						url: '<?php echo( esc_url( get_rest_url() ) ); ?>pmpro/v1/checkout_levels',
						dataType: 'json',
						data: jQuery( "#pmpro_form" ).serialize(),
						success: function(data) {
							console.log(data);
							if ( data.hasOwnProperty('initial_payment_formatted') ) {
								jQuery('#pmpro_live_price').html( "Total: " + data.initial_payment_formatted );
							}
						}
					});
				}, 500);
			}
			pmproUpdateLivePrice();
			jQuery(".pmpro_alter_price").change(function(){
				pmproUpdateLivePrice();
			});
		});
		</script>
	<?php
	return $param;
}
add_action( 'pmpro_include_cardtype_field', 'my_pmpro_live_price' );