Limit Review replies

If anyone is looking to implement this, I’ve figured it out. Adding the following code snippet will allow a reviewer and a post author to reply to one another. I have limited to 3 levels(initial comment, reply from post author, and follow up comment). You limit the levels in the threaded(nested) comments settings under “Discussions” in your WordPress settings.

/* Reply comment only allowed by post author */
add_filter( 'comment_reply_link', 'author_comment_reply', 10, 4 );
function author_comment_reply( $link, $args, $comment, $post ) {
	if ( isset( $post->post_author ) && $post->post_author ) {
		$user_ID = get_current_user_id();
		if ( $user_ID == $post->post_author ) {
			return $link;
		}

		// reviewer can reply to post author's reply
		if($comment->comment_parent) {
			$parent_comment = get_comment($comment->comment_parent);
			if ($user_ID == $parent_comment->user_id) {
				return $link;
			}
		}
	}
	return '';
}