Domain Mapping Not Working

I believe I have gone through all the correct steps to map a domain. I created an A record on the client's registrar account, pointing to the multisite IP.

After a couple of hours, the client's domain went to a blank page.

I went to the subdomain dashboard and mapped it to the new domain. When I enter the subdomain URL in the browser, it does change to the new domain, but it doesn't show the contents of the site, it just shows a blank page.

Help?

The multisite is PopCred.net

The client's site is readyforit.popcred.net.

I have deleted the domain map because my client is trying to work on the site.