Add Ajax Hooks and Call from Custom Template PHP

may be here is the error

add_action( 'wp_ajax_my_ajax_action', 'my_ajax_action_callback' );
add_action( 'wp_ajax_nopriv_my_ajax_action', 'my_ajax_action_callback' );

change to

add_action( 'wp_ajax_my_ajax_action_callback', 'my_ajax_action_callback' );
add_action('wp_ajax_nopriv_my_ajax_action_callback','my_ajax_action_callback' );

and in ajax change:

action : 'my_ajax_action_callback

go to functions.php and add:

require(dirname(__FILE__) . '/custom_template.php');   

make sure your ajax url is correct!!