Client (business owner) warned me about not receiving events notification.

When I checked the notification config, everything looks find, sent a test email and received correctly. But if I click on save, it shows error, it won't let save any change.

this is the html code:

<p>Hola 
  <strong>%employee_full_name%</strong>
</p>
<p>
  <br>
</p>
<p>Reserva confirmada para 
  <strong>%event_name%</strong> el 
  <strong>%event_start_date_time%</strong>.
</p>
<p>
  <br>
</p>
<p>Datos de la reserva:</p>
<p>
  <strong>%customer_full_name%</strong>
</p>
<p>
  <strong>%attendee_code%</strong>
</p>
<p>
  <br>
</p>
<p>

</p>
<p>
  <br>
</p>
<p>
  <strong>%company_name%</strong>
</p>
<p>
  <strong>%company_website%</strong>
</p>

Wonder if I need to set an organizer in order to receive notifications, because as isn't required...