Hello @Michele
Thanks for sharing the additional details.
To rule out any problems with the folder structure, it is recommended that you create the app using the fdk create command, referencing the appropriate template. In your case, the Your First Serverless App template should suffice. You should confirm that you can run this template app locally before copying your changes into this app and then trying to run it again.
If you still see the same error, can you please refer Freshworks CLI (FDK) now generates debug log file and share a verbose log file for the same?