I have read online it is possible to make a script/do small edits for whmcs that would change whmcs design depending on the referring website. i.e. so multiple domains can use the same whmcs with different designs (where whmcs is installed on only 1 parent domain).
main.com has whmcs installed
site1.com has design 1
site2.com has design 2
so lets call it sitex.com has design x
when sitex redirects to main.com, main.com (whmcs) design must change to designx + only display packages of sitex.
Don't mind if you use
or other solutions found on google. which ever is easiest.
Let me know if you can do this and price,