what site link to use

Hey guys.
Probably a stupid question, but I thought I’d confirm with you, first.

I’ve sales site set as .com (new build staging link above); with whmcs loaded to other domain name, hostbigspace.net.
Are there any special items/anything extra I need to do, in order to use the WHMCS setup on the .net domain, with the .com setup??
Or should I simply use hostbigspace.net/whmcs
OR!!!
Do I just use hostbigsapce.net?

Thanks in Advance~
Blake
(Yes, I’ve bought pro thru themeforest/codecanyon)

The page I need help with: [log in to see the link]