External URL not working on my HA app only?!

So I have the strangest of issues which I cannot solve. All of a sudden yesterday my External URL on my companion app (Android mobile) stopped working.

(08-16 20:05:59.768 31799 31799 E WebviewActivity: onReceivedError: errorCode: -2 url:https://URLMASK/).

I can however access this External URL through any other device and/or browser.

My partners app is working fine.

The external url on the companion app works if I’m not on my home WIFI (4G). Went into the office today and it works fine on work’s WIFI.

What is it about my WIFI network my phone/companion app doesn’t like about accessing the External URL?!?! Again I can access the URL through a web browser on my phone. I’ve tried rebooting the router.

Any help would be greatly appreciated!

The error is a name resolution issue…

Something is wrong with name resolution for that host on your internal network. How do you do internal DNS.

I’ve got a very layman’s setup. UK based, Sky Hub router provided by ISP.

Do you think it’s the way the router is locking down the DNS of my device?

Unsure there’s a bunch of reasons it could be.

You need to see what your phone gets as a response when it asks for your external URL. From the DNS server your router is telling your phone to use. Because it is either getting no response or a bad response. Once you figure that out you can continue troubleshooting