Plex in panel_frame do not succeed

Configuration
1

Did anyone succeed in adding plex-client to panel_iframe ?

I cannot understand why this does not work :

panel_iframe:
  stats:
    title: Grafana
    icon: mdi:chart-areaspline
    url: https://xxxxx.duckdns.org:xxxx/d/zQHJGwIWz/stroom_per_minuut?orgId=1
  plex:
    title: Plex
    url: https://xxxxxx.duckdns.org:xxxxx/web/index.html

The url works in a “normal” browser.
Port is open and forwarded to port 32400
Grafana has no problems
I allowed external portnumber as source port in Synology Nas.
Both plex server and HASS are in Docker containers