I want to create a webhook and on top of the payload ( event information data) I want to add extra parameters I tried a custom webhook template with different variables but none worked

{
  {{ default_webhook_data }},
  "custom_data": {
    "environment": "{{ env.ENVIRONMENT }}",
    "team": "{{ project.namespace }}",
    "deployment_type": "{{ ci_environment_name }}",
    "priority": "high"
  }
}

then

{
  {% include 'default_webhook_data' %}
  "custom_data": {
    "environment": "{{ env.ENVIRONMENT }}",
    "team": "{{ project.namespace }}",
    "deployment_type": "{{ ci_environment_name }}",
    "priority": "high"
  }
}

None of them worked leading to errors like :

Hook execution failed. Error while parsing rendered custom webhook template: unexpected character (after ) at line 2, column 5 [parse.c:804] in '{ {% include 'default_webhook_data' %} "CUSTOM_PROMPT": "How are you Claude today?" }

I tried to modify different template options,