Domain mapping – 403 forbidden error

Hi,
I am having a domain (example.example.com) with multisite feature enable and created two sites. So now in my network dashboard there are two sites named (example.example.com) and (example.example.com/site2). I tried to map example.example.com/site2 to something.something.com. Both has same A record pointing to same IP, also its a shared IP. But when i navigate to something.something.com after domain mapping it says 403 forbidden. I have seperate cpanel for both sites (example.example.com) and (something.something.com), not sure if this is a problem. What did i do wrong. Please help me to finish it.

Thanks,
Gnanasekar S.