The Compose file './docker-compose.yml' is invalid because:

Invalid top-level property "db". Valid top-level sections for this Compose file are: version, services, networks, volumes, and extensions starting with "x-".

You might be seeing this error because you're using the wrong Compose file version. Either specify a supported version (e.g "2.2" or "3.3") and place your service definitions under the `services` key, or omit the `version` key and place your service definitions at the root of the file to use version 1.

For more on the Compose file format versions, see https://docs.docker.com/compose/compose-file/