I have hosting from nexcess(http://www.nexcess.net) with dedicated IP pointing main site. I am running 3 sites on same host. I have used your domain mapping plugin and followed instructions to setup.Below are the steps...
1. I Installed WordPress MU Domain Mapping plugin.
2. Added define( 'SUNRISE', 'on' ); in wp-config.php file just before /* That's all, stop editing! Happy blogging. */.
3. Moved sunrise.php from Domain-mapping plugins folder to wp-content folder(moved not copied.However I have tried coping as well)
4. After this, I went to Network Admin >> Dashboard >> Settings >> Domain Mapping menu.
On next screen, I entered the IP address of my server .
6. I went into domain registrar(domain that need to be mapped) and add my dedicated IP address so that it can point main site.
7. Then I went into the individual site Dashboard >> Tools >> Domain Mapping. entered new Domain name and clicked "Map domain" button.
8. I get a message that says, "New domain added,"
9. Health status is "valid"
FYI: A wildcard sub-domain has already been created in my nexcess controll panel(wildcard sub-domain pointing to the main domain) .I also added parked domain in nexcess controll panel. Before adding parked domain, When I visit the new site, it was displaying not found error(404) and after adding parked domain, its redirecting to main site(https://example.com).
10. mod_rewrite is enabled in apache
Note: I do not have cpanel so please let me know what other steps I have to follow on nexcess control panel so that I can get work domain mapping for all sub sites.Please let me know if any other information required to resolve this issue.Thanks