SENDING webhooks

rest_command:
  example_request:
    url: "https://URL"

alias: Webhook Test
description: ''
trigger:
  - platform: device
    type: turned_on
    device_id: 12345
    entity_id: switch.basement_filter
    domain: switch
condition: []
action:
  - service: rest_command.example_request
mode: single

That format above works for me. The only thing I can think of is that you have an issue with formatting or your trigger is bad.