I find the IntelliJ documentation doesn’t exactly match what I want, so I’m going to list the steps I took here so I can refer back to them in future, and of course if others have the same issue then they will find this useful too.
. Open command window in relevant directory for the project you want to debug (the one with activator.bat in it).
. In the console, run “activator -jvm-debug” to find out the port to use (usually 9999).
. Then in IntelliJ, navigate to “Run -> Edit configurations -> Add new configuration”.
. Select “Remote”.
. Set “Port” textbox value to the port specified in step 1 (again, most likely 9999).
. Click the spider looking debug button at the top of IntelliJ.
. Back in the console, run the “run” command.
Once you’ve set a break point and navigated to localhost:9000 in your browser, you should be able to step through your code.