Yeah sorry :/ There isn't an iMessage API to talk to, so the only way that anyone has found to bridge with iMessage is to have an instance of macOS running, logged in as you, and to send messages through the iMessage app via AppleScripts and to watch the filesystem for incoming messages. It would be great if there were some API you could use to send messages through, but Apple has worked hard to keep iMessage locked down to Apple devices.
Having said that, I bought an old Mac Mini off of ebay for about $100, and it's been working pretty well for the past year or so. It's not an easy solution, but as far as I know it's the only solution for using iMessage on an Android or non-macOS desktop.
Having said that, I bought an old Mac Mini off of ebay for about $100, and it's been working pretty well for the past year or so. It's not an easy solution, but as far as I know it's the only solution for using iMessage on an Android or non-macOS desktop.