Would like Clarification If I'm Settings Up Domain Mapping Properly...

I'd like your feedback to see if I'm setting up domain mapping correctly as I haven't done it before. So I have...

domain.com = my WP multisite network primary domain
s1.domain.com
s2.domain.com
s3.domain.com
...and so on

On my network, subsites are set up via subdomain.

In my wp-config.php, I have these settings:

define( 'SUNRISE', 'on' );

/* Multisite */
define('WP_ALLOW_MULTISITE', true);
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', true);
//define('DOMAIN_CURRENT_SITE', 'domain.com'); <- disabled
//define('PATH_CURRENT_SITE', '/'); <- disabled
//define('SITE_ID_CURRENT_SITE', 1); <- disabled
//define('BLOG_ID_CURRENT_SITE', 1); <- disabled
define('WP_DEFAULT_THEME', 'defaulttheme');
define( 'NOBLOGREDIRECT', 'http://domain.com' );

Let's say user #2 purchased his own domain called domain2.com. He wants that to be mapped to s2.domain.com so that the contents is loaded when he enters domain2.com (not a redirection)

So he pointed domain2.com to my web host and I parked it to my host IP address. I double check the DNS records and see domain2.com's A record is pointed to the IP address of my server.

http://www.domain2.com is pointed to domain2.com

Now I log into the user's subdomain on my network (s2.domain2.com/wp-admin) and I access the Domain Mapping plugin settings and enter http://domain2.com as the custom domain and hit save.

Am I done here? Or am I missing a step?

Because by doing this, when I plug domain2.com into my browser, its still redirecting to s2.domain.com and shows "This webpage has a redirect loop". I did all this around 30 minutes ago, so I'm suspecting it may be a propagation issue so I'll wait a bit if that's the case.

Your feedback is appreciated. Thank you in advance!