Why is wp-admin/admin-ajax.php giving 0?

Question

PHP

Good evening.
I have a question, why is wp-admin/admin-ajax.php giving 0 ?
There is a NEX-Forms callback form, and when you click "Submit" AJAX does not fire, and it returns 0

Help. Why?
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This error is displayed only on the site on hoster.ru, everything is ok on the timeweb.
And I don't understand why. Files ONE TO ONE.

Answer 1

die(); at the end of the handler
And should be wp_ajax_nopriv_{action}
if the user is not logged in