Wordpress Multisite FQDN Admin Access

Question

I have a Wordpress multisite setup at http://in-autos.com and I have a sub-domain multisite structure and a FQDN http://billgattonsales.com

My trouble:
I can access the Admin area by visiting either the main site, or any sub-domain, but I cannot access the Admin area using the FQDN. So FQDN/wp-admin/ will not work.

What am I missing to get the FQDN/wp-admin/ to work correctly?

The DNS is forwarded, and the site works great from the home page, and sub-pages. Permalinks is working fine.

Server Setup:
I'm running the WP Multisite on a VM behind an Nginx router. Nginx appears to be functioning correctly.

Please tell me what you need. Thank you.

Access Log:

[10/Mar/2016:16:15:14 -0500] "POST /wp-cron.php?doing_wp_cron=1457644514.5484681129455566406250 HTTP/1.0" 200 20 "-" "WordPress/4.4.2; billgattonsales.in-autos" "-"
[10/Mar/2016:16:15:14 -0500] "GET /wp-admin/ HTTP/1.1" 302 5 "billgattonsales/wp-admin/" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:44.0) Gecko/20100101 Firefox/44.0" "-"
[10/Mar/2016:16:15:14 -0500] "GET /wp-login.php?redirect_to=billgattonsales.in-autos%2Fwp-admin%2F&reauth=1 HTTP/1.1" 200 1276 "billgattonsales/wp-admin/" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:44.0) Gecko/20100101 Firefox/44.0" "-"

After a few seconds, the screen is blank with no error codes. Error log is empty.

tail -f error.log produces no results.

Answer 1

In my experience WP doesn't like being accessed from anywhere that's not the site url in the wp_config table.

If you want to change the URL to your new(?) one this codex page should help, however it will probably prevent you from accessing by your old(?) url.