Problems Resolved (ex: Content-Length) - Use POST not GET!
I'm a little embarassed to admit that I have resolved my previous problems, and I now have a working endpoint with Node.js. The root problem was that I was expecting GET to the endpoint, while the Echo actually does a POST. I checked back to the docs, and they do say this, but I didn't read closely enough. And it wasn't obvious in any of my tests that this was the case. I have actually set up 3 different Node.js environments on the cloud, trying to get this to work. In all 3 cases, once I switched from app.get() to app.post(), the apps began working. Stupid me. Hopefully others with the same dumb error will find this post and save themselves some time. :)