Unable to login to new custom domain on multisite?

Question

Background

I setup WordPress Multisite a while ago. I added one on a custom domain, and more on subdomains of the main site. Since then I've added more on subdomains, and so far everything has worked fine.

Problem

I added another on a custom domain, and for some reason I cannot log into it. Each login attempt redirects to the login page again. All the other existing domains still work just fine.

What I Tried

I'm pretty sure it is cookie related. I was able to login once by resetting the password, but then it didn't login again. I've tried multiple browsers to see if that was the issue.

I checked the .htaccess to see if there were special directives for either of the custom domains, and didn't find anything. I compared the settings for both sites (from the Network Admin dashboard) and didn't see anything out of the ordinary.

Answer 1

Found the answer. I had not ran the Domain Mapping plugin before switching it to a custom domain. So the correct steps should look like this:

1. Create new site as a sub-domain (site.example.com)
2. Point sub-domain at root (example.com)
3. Point custom domain (site.com) at root (example.com)
4. Visit admin page for sub-domain (site.example.com)
5. Add custom domain (site.com) to Domain Mapping plugin
6. Visit custom domain (site.com)

I had forgotten step 5 and tried to just edit the site to be at the custom domain instead of the sub-domain.