testimonial is not displayed

I use testimonial on my homepage. I use a cache app and that’s why the testimonial is not varying (rand function). When I try to call the shortcode via ajax, the plugin returns an empty space.

The code:
if (shortcode_exists(‘tptpro’)) {
echo ‘Shortcode exists. ‘;
$shortcode_output = do_shortcode(‘[tptpro id=”27100″]’);
if ($shortcode_output) {
echo ‘Shortcode Output: ‘ . $shortcode_output;
} else {
echo ‘The shortcode did not return any content.’;
}

The code returns ‘Shortcode exists’ but [tptpro id=”27100″] does not return anything, only when it is not being called by ajax

The page I need help with: [log in to see the link]