Ajax : Why success displays 0?

I had a similar issue with admin-ajax.php returning 0, even i had die().

My problem was that the add_action was declared in a file not loaded default by plugin.

Anyway, if you have problem also check in browser what __.com/wp-admin/admin-ajax.php?action=youraction returns.

Try to add die(); or exit(); at the very last line of the function.

Found it.

It need to add die(); before the end of my own ajax function in function.php.

Because there is one line of script in admin-ajax.php after my own ajax_action that says: die('0'); So we need to die() script before die('0').

May be you are trying without login. so you need to use this action.

add_action('wp_ajax_nopriv_my_action', 'my_action_callback');

you will get response. :)