add button to content-single-listing-classifieds.php

I am wanting to add a button to the Listing Page next to the Contact Seller button that links to another page on the site called /guaranteed-diamond-transactions/
BUT I only want this button to show up if the item is in the category ID 280 /listing-category/diamond-rings/

I understand I need to code it within content-single-listing-classifieds.php , to use PHP code to add this condition with category ID.

I edited the PHP code on that page, I used this code but it didn’t work:


<?php
if ( in_category('diamond-rings') ) {
?>

<?php
}
?>


Can anyone help?