[ttiefenbach]

Thanks for the quick reply! Unfortunately, your code returned the topic’s title.

That allowed me to narrow my search, though, and I was able to get the correct functions for my permalink structure:

function my_filter_thumbnail_id( $thumbnail_id, $post = null ) {
	if ( $post->post_type != 'topic' )
		return $thumbnail_id;
	
	$forumid = bbp_get_topic_forum_id();
	if ( $forumid == 6728 )
		$thumbnail_id = 7091;

	return  $thumbnail_id;
}
add_filter( 'post_thumbnail_id', 'my_filter_thumbnail_id', 20, 5 );

I could probably use the bbp_get_forum_title() function to get the tiel to compare, like you suggested, but I went with just validating the ID since it was working.

Thanks for your help!!