This checks to see if the post being loaded is 1. a special offer 2. if the dealer is authorised to load the special offer on their dealer site and if not we force a 301 redirect back to the dealers home page

functions.php

<?php
######################################################
//Here we will check to see if the special offer being presented
//is in the list of the dealers posts and if not do a 301 redirect
//back to the home page
//added on 19/10/2018 by [email protected]
######################################################
function white_label_special_offer_301_redirect_check($array_of_dealer) {

	###################################################
	//STEP 1
	//Make sure the post type is special-offer.
	//If not stop the function in order to save resources.
	###################################################
	if(get_post_type(get_the_ID()) != "special-offers") {
		return;	
	} 
	
	###################################################
	//STEP 2
	//Get a list of the post id's for this dealer from array_of_dealer.
	//This list is created through white_label_get_array_of_special_offer_posts_for_dealer()
	###################################################
	$array_of_dealer_special_offers = $array_of_dealer["OtherData"]["dealer_special_offers"];
	
	//if there are no posts at all, then we need to 301 redirect right away
	//as this post should not appear on the 
	if(count($array_of_dealer_special_offers) == 0) {
		header("HTTP/1.1 301 Moved Permanently"); 
		header("Location: /"); 
		exit;
	}
	
	###################################################
	//STEP 3
	//Now we need to check if this post id exists in the list of
	//$array_of_dealer_special_offers and if not, 301 redirect.
	###################################################
	$this_post_id = get_the_ID();
	
	if(!in_array($this_post_id, $array_of_dealer_special_offers)){
		header("HTTP/1.1 301 Moved Permanently"); 
		header("Location: /"); 
		exit;
	}
	
	//thats it, nothing else to do here
	return;

}