mapping a subdomain using domain mapping plugin


can I map into a multisite

I have used doamin mapping with tlds I own and control the DNS and can point them to the correct server, then uses A record to point the ip and then parked the domains in cpanel and it works fine, but this time I want to point a client's subdomain over into a subdirectory site within my multisite and run that for them.

I set up an A record on their cpanel for and pointed it to my server ip, then tried to set their sub up as a parked domain but ran into an error regarding their DNS, so I figured this might be done via a CNAME record but again ran into an error re Fully qusalified domain, and at that point I'm needing some help - can this be done as described..