How to show featured image custom post type?

Hello guys,

Can someone please give me a little help here?

I need to show a custom post type feature image in my single.php.

I am trying this code:

<?php the_post_thumbnail('freeGallery', array('class' => 'imgthumb')); ?>

PHP:

But without success...
It shows the normal post featured image (single.php) and not the custom post (freeGallery) featured image.

I also tried:

<?php the_post_thumbnail('galleryhover'); ?>

PHP:

Adding this to functions.php

add_image_size( 'galleryhover', 240, 360, true );

Code (markup):

The only problem here is that is showing the normal post featured image (single.php) and not the custom post (freeGallery) featured image.

HELP

What I'm doing wrong?

Thanks!!