Finally, I figured out how to solve the subdomain and reports 403 forbidden error.
This is ALL about the file system permission.
Firstly, for domain reports:
This folder chmod was: drwxr-x---
You could see there's NO read and execute rights for others.
When I change it to drwxr-xr-x
All domain reports WORKS.
Similarily to subdomains,
There are 2 folders: cgi-bin and httpdocs
It is necessary to ensure all folders must need to have read and execute rights for others.
I m not 100% sure if I change these permission on the file systems is the best solution or not.
At least it is the most simplest and clear cut method.