src/IronMQ.php
public function deleteMessage($queue_name, $message_id, $reservation_id = null)
    {
        $req = array(
            "reservation_id" => $reservation_id,
        );
        $this->setJsonHeaders();
        $queue = rawurlencode($queue_name);
        $url = "projects/{$this->project_id}/queues/$queue/messages/{$message_id}";
        if (is_null($reservation_id)) {
            return $this->apiCall(self::DELETE, $url);
        } else {
            return $this->apiCall(self::DELETE, $url, $req);
        }
    }
public function deleteMessage($queue_name, $message_id, $reservation_id = null)
    {
        $req = array(
            "reservation_id" => $reservation_id,
        );
        $this->setJsonHeaders();
        $queue = rawurlencode($queue_name);
        $url = "projects/{$this->project_id}/queues/$queue/messages/{$message_id}";
        if (is_null($reservation_id)) {
            return $this->apiCall(self::DELETE, $url);
        } else {
            return $this->apiCall(self::DELETE, $url, $req);
        }
    }
Delete a Message from a Queue
This call will delete the message. Be sure you call this after you’re done with a message,
or it will be placed back on the queue.

@param $queue_name
@param $message_id
@return mixed