So here’s something to consider…
You have an app, that app talks to your servers via some authenticated protocol, and I’m assuming it’s using our user auth so that we can’t just guess a device id and get someone else’s data, right? Is that not an API?
So, you already have an API and a user auth method, you just need to release some documentation for it. Being able to integrate with HASS and OpenHAB and SmartThings and others would be a huge selling point for you. You don’t even have to document the whole API, just the auth and data fetch.