Help getting custom actions to work

Hi, I am trying out the “custom actions” feature but can not get it to work.
I have started a simple python http server with “python3 -m http.server” and using the url “http://localhost:8000/” in a browser produces some logs from the server and lists the cwd contents in the browser. So far so good. I then created a custom action and entered the same url. A context menu item is now showing when right clicking an asset but nothing happens when I click it. There is no output from the python server and there is no logs on the developer page.
Using “Developer tools” in my browser I can see this error in the console:
POST 422
originating from raven.js:377 and a failed request with the preview:

  1. {type: “error.list”, request_id: “0001onnvvvt4a0vk2r30”,…}
  2. errors: [{code: “422”, message: “Cannot have more than 200 active event names”}]
  3. request_id: “0001onnvvvt4a0vk2r30”
  4. type: “error.list”

I am not sure where to go from here so any help would be appreciated. Thanks