IW4x has a new website that hosts the internal API used to manage the master server, along with more detailed guides specific to IW4x than those available on this forum.
Check it out at: iw4x.dev
There is also an outdated wiki for IW4x, which will eventually be migrated to the new iw4x.dev website.
The current tutorials available on this forum in the Docs section are still up to date and valid. Some of the information here has not yet been ported to the new website, so make sure to check both before asking for support.