Yes, for the certificate creation, I can see your point. Anyway, it is what it is. HTTPS is required, you need a certificate with chain of trust. There’s nothing we can do to support your setup. Sorry.
Where is the requirement for chain of trust coming from? I know of no other program or app that will not work with self-signed certificates if you confirm you want to trust them or install them on your phone.
Using self-signed for my NAS and everything can connect to it.
SSLForFree.com: Do these SSL certificates work for IP addresses?
No, certificates can only be generated for registered domain names.
Same for Let’s Encrypt.
This is not going to be easy 
We are the same. We use self-signed certs locally and install our root trust certificate on machines locally. It did not work for Garmin. You need to search for the details of this answer elsewhere online, we’ve told you how to make it work. That’s the end of our technical support I’m afraid.
Self-cert does not work for me even when I have installed the root trust jobbie on my Android phone, Let’s Encrypt does.
If you find the answer to how to make this work with self-signed certificates and Garmin’s SDK please post back here.
Good luck.
One thing that does work is communicating through wifi directly.
The app API Call allows the user to force wifi usage. It temporarily enables wifi until the data is done exchanging.
This should work for Home Assistant also. When opening the app, wifi is enabled and then stay enabled until HA is closed again.
Hust an idea while I try to get Let’s Encrypt to work.
Not for me. I had to “synchronise” to start Wi-Fi. No direct Wi-Fi on offer, probably because its power hungry and hence not a great idea.
Please post details as I have not found that. The only lead I have followed has been a productive hack in the simulator and then messed up my watch when deployed for real. Difference between simulation and real life…
Check out this app from the Garmin Connect IQ Store Connect IQ Store | Watch Faces and Apps | Garmin
media [optionnal]
Type : String [“BT”|“WIFI-LTE”]
Default : not defined
Description :Force the media that is used to send the request. If you use this option, the specified option will define the only media that will be used. If not defined, the default behavior is to use Bluetooth if connected, else try WiFi/LTE. Trying WiFi can can be disabled in general options of the widget. This option take precedence on general options.
Note that, unlike Bluetooth, WiFi/LTE doesn’t require HTTPs, force Wifi is a solution if you can only use HTTP.
Example :
With {…,media:“BT”}, Bluetooth will be used if connected, but WiFi will never be tried even if the general option “Use Wifi/LTE if bluetooth unavailable” is enabled.
With {…,media:“WIFI-LTE”}, only WiFi/LTE will be used.
Sounds like the developer has solved the problem, but does not publish the source code so hard to see how. Have you tried making contact to see if (s)he’s willing to share?
I’ve a few other jobs on presently.