AJAX with WP_Session [Read Details.html here for details]

custom.js

jQuery( '.click' ).on( 'click', function() {

	var post_id = jQuery( this ).attr( "data-id" );
	var thisis = jQuery( this );

	jQuery.ajax({

		url: postcustom.ajax_url,
		type: 'post',
		data: {
			action: 'vg_show_post_id',
			post_id: post_id,
		},
		success: function( response ) {
			jQuery( thisis.next( '#after-ajax' )  ).fadeIn( "slow" );
			jQuery( thisis.next( '#after-ajax' )  ).text( "Item is added to the cart!" );
			jQuery( '#session-sidebar' ).html( response );
			jQuery( thisis.next( '#after-ajax' ) ).fadeOut( "slow" );
		}

	});

});

Details.html

The concept is to put a Button in Post Content which the user will click. 

Two things - The ID of the post and Number of times the user clicks the Button should be displayed.

Underlaying Reason - With this we are presenting Posts as Products and with that button user can add products, 
and number of clicks on the button will signify the quantity that he wants.

The logic is working well with the normal php session, but not working with WP_Session.

Working php session - https://gist.github.com/vajrasar/8a8aa97de1b39f18ef29

Using WP_Sessions it sucessfully displays what it should the first time when the button is clicked but never on multiple clicks. Never.

functions.php

<?php

/*****************************
*
* Ajax Stuff
*
********************************/

function vg_session_start() {
	global $wp_session;
	global $cart;
	global $counter;

	$wp_session = WP_Session::get_instance();

	if( !empty( $cart ) ) {
		$cart = $wp_session['wpscart']->toArray();
	  echo "<br />" . "Not empty cart -in init";
	}
}
add_action( 'init', 'vg_session_start' ); // Starting Session

function ajax_test_enqueue_scripts() {
	wp_enqueue_script( 'customjs', get_stylesheet_directory_uri() . '/js/custom.js', array('jquery'), '1.0', true );
	wp_localize_script( 'customjs', 'postcustom', array(
								'ajax_url' => admin_url( 'admin-ajax.php' )
							));
}
add_action( 'wp_enqueue_scripts', 'ajax_test_enqueue_scripts' ); // Enqueueing Scripts

function vg_after_entry() {
	?>
	<button type="button" class="click" href="#" data-id="<?php echo get_the_ID(); ?>">Submit</button>
	<div id="after-ajax">
		<!-- to do post ajax stuff -->
	</div>
	<?php
}
add_action( genesis_entry_footer, vg_after_entry ); // Adding button in post content

function vg_show_post_id() {
	global $wp_session;
	global $cart;

	$wp_session = WP_Session::get_instance();

	$cart = $wp_session['wpscart']->toArray;

	$p_id = $_REQUEST['post_id'];
	$title = get_the_title( $p_id );

	if ( defined( 'DOING_AJAX' ) && DOING_AJAX ) {

			if ( !empty( $cart ) && array_key_exists( $p_id, $cart ) ) {

				$cnt = $cart[$p_id];
				$cnt++;
				$cart[$p_id] = $cnt;

			} else {

				$cart[$p_id] = 1;

			}

			foreach( $cart as $key=>$value ) {
				echo "<br />" . get_the_title( $key ) . " " . $value . " units";
				echo "<hr />";
			}
			
			$wp_session['wpscart'] = $cart;
			die();

	} else {
		echo "Not in admin-ajax";
	}

}
add_action( 'wp_ajax_nopriv_vg_show_post_id', 'vg_show_post_id' ); // for ajax
add_action( 'wp_ajax_vg_show_post_id', 'vg_show_post_id' ); // for ajax