Symfony variable does not exist

I want to display a welcome message for an appointment when the startdate is near (the function is built with js). Now for the view: The data that is in the message comes from another entity which is related to by use of a join-column. Now i cant use a loop through the appointments because this wil show the message for all the appointments regardless of what the startdate is.

this is is my appointment entity

/**
* @ORMEntity
* @ORMTable(name="appointments")
* @ORMEntity(repositoryClass="AppBundleRepositoryAppointmentRepository") */    

class Appointment
{

/**
 * @ORMManyToOne(targetEntity="Client")
 * @ORMJoinColumn(name="client_id", referencedColumnName="id")
 */
protected $client;

/**
 * @ORMManyToMany(targetEntity="ClientEmployee")
 * @ORMJoinTable(name="appointment_clientemployee",
 *      joinColumns={@ORMJoinColumn(name="appointment_id", referencedColumnName="id", onDelete="cascade")},
 *      inverseJoinColumns={@ORMJoinColumn(name="clientempoloyee_id", referencedColumnName="id", onDelete="cascade")}
 *      )
 */
protected $clientEmployees;

This is my client entity

/**
* @ORMEntity
* @ORMTable(name="client")
* @ORMHasLifecycleCallbacks
*/
class Client
{
   /**
  * @ORMManyToMany(targetEntity="ClientEmployee", cascade={"remove", "persist"})
 * @ORMJoinTable(name="client_client_employee",
 *      joinColumns={@ORMJoinColumn(name="client_id", referencedColumnName="id")},
 *      inverseJoinColumns={@ORMJoinColumn(name="client_employee_id", referencedColumnName="id", unique=true, onDelete="cascade")}
 *      )
 */
protected $clientEmployees;

/**
 * @ORMColumn(name="path", type="string", length=255, nullable=true)
 */
private $path;

This is the HTML(im using twig templating)

<div class="message-overlay">
    <div class="message-box">
        <p>Van harte welkom</p><br>
        <p> {{  appointment.client_client_employee.firstname }}</p>
        <div class="greeting-box" style="background-image: url({{ asset('bundles/app/img/dots-repeat.png') }});">
            <img class="message-embleem" src="{{ asset('bundles/app/img/Lameco_Icon_1.png') }}"/>
        </div>
        <div class="image-box">
            {#<img src="{{ asset('/../../../../web/' ~ client.path) }}"/>#}
        </div>
    </div>
</div>