How to scripts in V3?

I am trying to create an extension following the example here: 

https://github.com/google/extra-keyboards-for-chrome-os/blob/af3d693fa18c76c2e0161267d5b3b8624c621d83/example/remap/manifest.json#L6

But I got this error:


The "background.scripts" key cannot be used with manifest_version 3. Use the "background.service_worker" key instead.
Could not load manifest.