[Plugin: WordPress MU Domain Mapping] Can’t get to Backend of Mapped Subdomain Blog

I hope someone can point me in the right direction. I have MU installed in the root of https://example.com which is in a Cpanel environment. I have created a wildcard subdomain (*) and have created a subdomain blog at https://site1.example.com. This is working normally.

I have a domain in GoDaddy named https://site1.com that I want to map to https://site1.example.com. These are the steps I’ve followed to get this working:

Installed MU Domain Mapping, moved sunrise.php, uncommented sunrise in wp-config.

In Site Admin–>Domain Mapping I added my server IP address.

In the Backend of the subdomain blog of https://site1.example.com I added the domain name of https://site1.com (and think I checkmarked “Primary domain for this blog”).

I went into Cpanel for this MU install and went to “Simple DNS Zone Editor”, chose my MAIN INSTALL DOMAIN (https://example.com) and added an A record using my IP address.
***Please note that the wording in my Cpanel was a bit different from the Cpanel instructions here.***

I then went into my GoDaddy domain manager and changed the nameservers of the https://site1.com domain to point to my MU hosting account.

It’s sort of working, but something is wrong because I can’t get to the backend of the subdomain blog any longer. Let me explain. If you go to https://site1.com the contents of https://site1.example.com are showing. However, when I try to login, either from the mapped domain, the subdomain, or click the “backend” link from within the Site Admin—>Blogs area, I am always redirected to https://site1.com/wp-admin/ and I’m getting my 404 page.

If I visit https://site1.com/wp-login.php I am redirected to https://site1.example.com/wp-login.php. I’m not sure if this is intended behavior by the plugin or not, but if I login here, again I am redirected to https://site1.com/wp-admin/ and I get the 404.

Can someone tell me if I might have something configured wrong, or what else I could check? Any assistance would be great appreciated. Thanks for your time.