public function AddSubscriberToList($emailAddress, $listIDs, $subscriberKey = null)
    {
        $newSub = new ET_Subscriber;
        $newSub->authStub = $this;
        $lists = array();

        foreach ($listIDs as $key => $value) {
            $lists[] = array("ID" => $value);
        }

        //if (is_string($emailAddress)) {
        $newSub->props = array("EmailAddress" => $emailAddress, "Lists" => $lists);
        if ($subscriberKey != null) {
            $newSub->props['SubscriberKey']  = $subscriberKey;
        }

        // Try to add the subscriber
        $postResponse = $newSub->post();
        if ($postResponse->status == false) {
            // If the subscriber already exists in the account then we need to do an update.
            // Update Subscriber On List
            if ($postResponse->results[0]->ErrorCode == "12014") {
                $patchResponse = $newSub->patch();
                return $patchResponse;
            }
        }
        return $postResponse;
    }