The "Site Address (URL)" setting is the address you want people to type in their browser to reach your WordPress blog.
The "WordPress Address (URL)" setting is the address where your WordPress core files reside.
from this reference:
https://codex.wordpress.org/Changing_The_Site_URL
And all of that assumes the DNS all set up correctly. I suspect you first need to check your namservers and dns zones for both domain and make sure the domain resolves to the IP address of the host where the site finally will reside. Good Luck