Send failed error
Open the URL from your client config in the browser on the same device and see what happens. Also check server logs after.
That is what I said I did in my original post. The url from the client config works in a browser on the client device but not in the app. They're all iPhones, 13 Pro, Xs, X and a 7. One of the 13 pro devices is the 1st one I setup and it works in the client app and browser. All the rest only work in a browser when using the url but internal ip address works in app and in a browser. When using the url in the app, there are no corresponding HEX messages in the logs.
What's the URL?
I figured it out. It was a port forwarding issue where the initial device I had setup was using a tunnel and the other devices weren't and port 5001 was closed on my firewall.
It does not explain this:
The url from the client config works in a browser on the client device but not in the app.
Getting "Send failed" errors when using publicly accessible domain on additional devices. The initial client device I setup works fine on both internal ip and url but additional devices will only send when internal ip is used. No HEX messages in the log when attempting with url suggests it can't see the server this way but I can access the server via the url on Safari on the device. Any help would be appreciated.