I’m not familiar with the code base you’re using. I found issues with Tradovate’s code personally.
but you also need 2 new lines before the body. see my example. (it looks like you are passing 2 new lines from the console output but it’s hard to tell given the last couple of lines
if you want a working example you can look at the web console of a running browser after logging in. navigate to the websocket connection to view the data going back and forth. subscribe to new data in the website… and voila… you see the whole cycle. Their webapp uses the api except slightly different urls