I have set up a slave site as a subdomain to my master site. But I have a separate domain name that I want to use for the slave site, so it doesn't show the master site's domain name. Right now I'm doing a simple PHP redirect from the slave domain name to the subdomain on the master site:

www.slave.com -> PHP Redirect -> slave.master.com

But I want my slave domain to continue showing, along with the entire URL string:

www.slave.com/my-listings/listing123

The only way I think I know how to do this is do domain forwarding with masking, but it is my understanding this is not proper in SEO terms.

What do you recommend?

Thanks!

I don't know if you are using cPanel or other admin tool but I will assume this is cPanel.
In cPanel, you have to create an AddOn domain where you provide the "document root" with the same path as the one that you have provided to your subdomain "slave.master.com"

So that they will become synonym for your HTTP Server.
Do not use "redirection" in your HTTP Server because this change the URL and JMS Multisites will not know the original URL (lost).

Don't forget to add the "www.slave.com" in your JMS Multsites "slave.master.com" sliave site definition. It must also be present in the list of domains.

Thanks Edwin! I had done all of that except add the slave domain name to the list of domains - worked great!