Some technical question here , frustrated that no one from Unifi or Maybank is unable to answer it

I just subscribe to Biz5 package. I am using this service inside a shopping mall. From what i understand, the Unifi line goes through the mall's phone line instead of fiber optic line from a residential lot.

The question is i applied for a credit card merchant terminal and the installer came to fix it but it was unable to use the phone line. Is there a reason to it? Do i need to add another fixed phone line in order to be able to use the credit card terminal?