Iframe panel not working

I am trying to add access to my pihole container (created with docker CE and shown in the portainer addon) using iframe-panel. My configuration entry is:

panel_iframe:
  pihole:
    title: "PiHole"
    url: "http://192.168.254.200/admin/"  

Neither home assistant or pihole is https. the url in the configuration above works correctly.

PiHole shows on the left panel in HA, but when I click on it, I get:

192.168.254.200 refused to connect.

where have I gone wrong…or is panel not working or does panel iframe not work with URL/xxxx ?

Note: I have updated all software to latest. Environment is Debian 10, docker, HA.