I am trying to run asmbb on a caddy web server on docker using the following configuration

caddy.asmbb:80 {

	reverse_proxy {
	    transport fastcgi unix//var/www/asmbb/engine.sock {
		    capture_stderr
	    }
	}
	
	file_server 
}

Running engine in a docker container:

docker compose exec -it caddy sh
/srv # ps
PID   USER     TIME  COMMAND
    1 root      0:00 caddy run --config /etc/caddy/Caddyfile --adapter caddyfile
   23 root      0:00 ./engine
   26 root      0:00 sh
   32 root      0:00 ps

/srv # ls -al /var/www/asmbb/
total 2420
drwxr-xr-x    4 root     root          4096 Jul 18 16:52 .
drwxr-xr-x    3 root     root          4096 Jul 18 16:50 ..
-rw-r--r--    1 root     root           106 Jun  6  2023 .htaccess
-rw-r--r--    1 root     root         13512 Jun  6  2023 License.txt
-rw-r--r--    1 root     root             0 Jul 16 01:28 asmbb_ipc.lock
-rw-r--r--    1 root     root             0 Jul 16 01:28 asmbb_queue.lock
-rw-r--r--    1 root     root        397312 Jul 16 01:28 board.sqlite
-rw-r--r--    1 root     root         32768 Jul 18 16:52 board.sqlite-shm
-rw-r--r--    1 root     root        156592 Jul 18 16:52 board.sqlite-wal
-rwxr-xr-x    1 root     root        157818 Jun  6  2023 engine
srw-rw-rw-    1 root     root             0 Jul 18 16:52 engine.sock
drwxr-xr-x    5 root     root          4096 Jul 16 01:24 images
-rw-r--r--    1 root     root          6833 Jun  6  2023 install.txt
-rwxr-xr-x    1 root     root        808756 Jun  6  2023 ld-musl-i386.so
-rwxr-xr-x    1 root     root        861496 Jun  6  2023 libsqlite3.so
-rw-r--r--    1 root     root          1204 Jun  6  2023 lighttpd.conf
-rw-r--r--    1 root     root            41 Jun  6  2023 manifest.uuid
drwxr-xr-x    8 root     root          4096 Jul 16 01:24 templates

When trying to access the site:

curl -I http://caddy.asmbb
HTTP/1.1 503 Service Unavailable

In the caddy logs:

"status":503,"err_id":"idvuzb2i2",
"err_trace":"reverseproxy.(*Handler).proxyLoopIteration (reverseproxy.go:486)"

Has anyone configured asmbb on a caddy?