Docker compose run throws error on entrypoint

In the abiosoft/caddy Dockerfile, the standard entrypoint is ENTRYPOINT ["/bin/parent", "caddy"] (link here).

So I think that you must change ./caddy in your entrypoint by /bin/parent caddy.

I also think that you don't have to overwrite the default entrypoint, you just have to specify your args to caddy by overwriting the default command (which is CMD ["--conf", "/etc/Caddyfile", "--log", "stdout", "--agree=$ACME_AGREE"]).