Cannot run Ocsigen app: "...ocsigenserver/var/run/ocsigenserver_command. I will continue without."

I'm on macOS Sonoma (M2), with ocaml 5.2.0 etc installed via opam (not using Homebrew). Then wanted to give Ocsigen a try.

First install ocsigen:

opam install ocsigenserver

Then create the project:

dune init project mysite

Adjust the dune file:

(executable (public_name mysite) (name main) (libraries  ocsigenserver  ocsigenserver.ext.staticmod))

The rest can be found on this page. Calling dune exec mysite failed:

$ dune exec mysitemysite: ocsigen:main: Cannot create the command pipe /Users/andretampubolon/.opam/5.2.0-flambda/lib/ocsigenserver/var/run/ocsigenserver_command. I will continue without.: Unix.Unix_error(Unix.ENOENT, "mkfifo", "/Users/andretampubolon/.opam/5.2.0-flambda/lib/ocsigenserver/var/run/ocsigenserver_command")

Here's my repo. What's wrong here?