All connections work except the iOS app

Mobile Apps Home Assistant Companion for Apple
1

I’ve installed duckdns and wireguard. I can get to HA from everywhere, including remotely, with Safari. The VPN is working remotely across my local network as expected. But I can’t get to HA from the app. With https the error I get is NSURLError - domain 1202.

I’m stumped. Obviously is a cert error, but why just the app?

aliases: []
domains:
  - xxxxxxxx.duckdns.org
lets_encrypt:
  accept_terms: true
  algo: sxxxxxxxx1
  certfile: fullchain.pem
  keyfile: privkey.pem
seconds: 300
token: 6xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx4

peers:
  - addresses:
      - 172.27.66.2
    allowed_ips: []
    client_allowed_ips: []
    name: hassio
  - addresses:
      - 172.27.66.3
    allowed_ips: []
    client_allowed_ips: []
    name: donsiphone
  - addresses:
      - 172.27.66.4
    allowed_ips: []
    client_allowed_ips: []
    name: donsmb
server:
  addresses:
    - 172.27.66.1
  dns: []
  host: xxxxxxxxx.duckdns.org

configuration.yaml
http:
  ssl_certificate: /ssl/fullchain.pem
  ssl_key: /ssl/privkey.pem'