First, I launched a server on my mac.
Then, I created an App in the GHL app marketplace.
I was able to grant my server permissions via the App...
And make updates into my clients subaccount via the OAuth2.0 API
Today, I got the server moved from my computer to a hosting rool online (Render.com) And now it's live, pinging the client's 3rd party LOS and updating his subaccount with new data.
I knew this was all possible, but didn't know how freaking easy it was to actually build...