i got this message in backoffice, not sure if its a problem of controller.cs, or controller.js, thanks 🙂

It's very hard to give an answer based on an error message alone. The only thing I can tell you is you might be able to see more info in your browser developer tools (in the console, or on the failing network request). The best way to get help is to tell us more about your journey, the things that led to you seeing this error. What happened before?