@javi I've been using ngrok.com, which makes it very easy to temporarily give something running locally a domain name that anyone from outside (including other servers, obvs) can use to access your site/app and send Activitys.
e.g. https://piefed.ngrok.app is running off the laptop in my office. Any code edits immediately take effect and I can watch errors scroll by in my IDE in real time, set breakpoints, etc. Very effective.