For WITW, Firefox dev tools has more possibilities than those of Chromium (and for others if they need this one day).
* On the client, open dev tools (CTRL-SHIFT-i),and dock it to the bottom of the screen,
* click "Debugger" on the top bar,
* unfold "Main Threadé (at the left) and click on the server's name,
* at the right, go down until you found "Event Listener Breakpoints" and unfold it,
* at the right of "Event Listener Breakpoints", check "Log",
* also check: "Websocket" and "XHR" below,
* reload the page
This way, all WS traffic appears underneath, saying: bla, bla, "open { target: WebSocket isTrusted: true", etc…
JY