Port 2342 is PhotoPrism’s own default port, but on Syncloud PhotoPrism is not exposed on it. It runs behind the platform web server on the normal HTTPS port, so the firewall rule for 2342 is not needed and you can remove it.
In PhotoSync’s PhotoPrism target use:
Host: photoprism.[your domain]
Port: 443
HTTPS: on
Username / password: your Syncloud username and password
Your existing WebDAV setup keeps working too, at https://photoprism.[your domain]/originals/ with the same Syncloud credentials.
Let me know if PhotoSync still cannot connect after that.