Not sure if you figured it out or still need help, I happened to be trying to do the same thing. I configured everything in services.yaml as below (all specifics removed).
services.yaml
- Hosted Services:
- Unraid:
icon: unraid.png
href: http://host.ip
description: Unraid host
ping: host.ip
statusStyle: 'dot'
- Sonarr:
icon: sonarr.png
href: http://host.ip:port
description: Sonarr
widget:
type: sonarr
url: http://host.ip:port
key: <your_api_key>
siteMonitor: http://host.ip:port
statusStyle: 'dot'
With the ping approach, when hovering over the green dot I get "Ping Up (0ms)" and wtih the siteMonitor it "HTTP Status 401 (14ms)", I'm assuming thats because Sonarr isn't liking the way the request is being sent (not sure about this, need to do more research).