Get custom Session value on another page in wordpress template

I'm trying to make SESSION in wordpress and use my session value on another custom wordpress template. For Example:I'm trying to transfer value <?php $_SESSION['post_data']= $_POST['payvalue']; ?> from one page to another on Wordpress template but can't get it working. After submit from First page to Second page Session array on second page appears to be empty. On Second Page I print <?php print_r($_SESSION); ?> but it returns empty array.

I've already inserted session_start() at all page.

How can i use my custom session value on second page in Wordpress template?

via Chebli Mohamed