WordPress and multisite functionality issues

I've been using WordPress and the multisite feature for a while, but am not quite sure if I've ever successfully configured multisite on a subdomain.

• Main site:mainsite.com(not WordPress)

• Substation:community.mainsite.com(Using WordPress Multisite)

• Sub-sites:demo.community.mainsite.com, has been created in a multisite with network administrator privileges.

• Add TXT records for domain verification.

• Create a new domain alias. If you map a sub-site to a custom domain name (such as the demo.customdomain.com), I also need to add that custom domain.

Even though I have configured the sub-site as per the above steps, when trying to access the demo.community.mainsite.com When it does, it doesn't open properly. I hypothesize that it may be a DNS configuration issue, but I can't find out exactly why at this time.

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