httpd serving php

Dear support team,

in a OpenBSD 6.3 installation with php packges added, I have the
following httpd configuartion:

server "domain" {
listen on * tls port 443
listen on :: tls port 443
tls {
certificate "/etc/ssl/private/server.pem"
key "/etc/ssl/server.key"
}

directory index index.php

location "/pub/*" {
directory auto index
}

root "/htdocs/domain"

location "*.php" {
fastcgi socket "/run/php-fpm.sock"
}
}

the above generates a 500 error!

Also, no '/run/php-fpm.sock' exists!

Thank you for your help