Please refer to https://developers.topdesk.com/documentation/index.html and https://www.zabbix.com/documentation/5.0/manual/config/notifications/media/webhook#example_scripts.
  
Set global macro {$ZABBIX.URL} with your Zabbix server URL.
Add a dedicated user with the media type "TOPdesk".
Change the values of the variables topdesk_api (URL), topdesk_password, topdesk_user. The topdesk_status is the default status for creating a new TOPdesk ticket.