I get following notice in WordPress

Notice: Undefined index: _wpnonce in /var/www/vhosts/abc.biz/php/func.php online 338

Any solution? Thank you for help

I discovered the answer, need to use isset() to check on _wpnonce value, before evaluating it.

if ( isset($_POST['_wpnonce']) && $_POST['_wpnonce'] = '123456789' ) {}

Thanks.