I was trying to integrate my Actions-on-Google assistant app with OAuth 2.0. It wasn't working and I was playing around with the UI flipping switches to find out what would work. When I inactivated the app, I couldn't re-activate it!
The error message is 'Your app must have at least one action to test' (screenshot). But the app is fully functional and I could test it before inactivating. The app code is here for reference.
To be sure that I haven't messed up anything else, I also inactivated another similar project number-genie that I had successfully working and that too cannot be activated again and shows the same message!
How can I reactivate the simulator for testing?
Usually Actions will become inactive after some period of time (this used to be 30 minutes, but I'm not sure if that is the current timeout).
You can go back to API.AI and re-click on the Test button to have it re-deploy for the simulator. You can then make it active again.