For some extensions I'd need to use third party/generic sip clients rather than the 3cx client. So I'm testing this setup with an extension and the Telephone app on macOS. I've copied ID and the password from the extension Authentication box and used the <custom>.3cx.us domain name, however the client displays the 404 error upon registration attempt. I have the "disallow use outside LAN" unchecked -- any other setting I missed that is needed for the 3rd party SIP client to work? Another client I'd need to use is the Linksys/Cisco SPA box I use in home automation, but I'm not at its location yet -- anything else needs to be configured differently for that box?