shortcode isn’t work in php

Hi,
the shortcode isn’t work on php like that

<?php
$checkwa= do_shortcode(“[whatsapp_number]”);

if($checkwa==””)
{
echo “no Whatsapp Number”;
}
else
{
[ht-ctc-chat];
}
?>

… we also try with do_shortcode:
echo do_shortcode(‘[ht-ctc-chat]’);
like here:
https://wordpress.org/support/topic/shortcode-show-the-text-ht-ctc-chat/
but it doesn’t work !?

Thanks & Regards
Dieter