You cannot play media or invoke steps that require an active contact (e.g. Accept) if you are doing an offline step-through debug within the CCX editor. For this you would need to perform a reactive debug instead.
Upload the script and assign it to an application.
Start a reactive debug on it.
Call a trigger for the application.
The script will appear in the editor and allow you to walk through it. The difference is that you now have a contact (yourself) in the script and can hear the output.