Glide's Custom Domain Wizard assumes your subdomain is only one level deep. However, if your custom domain has nested subdomains, the wizard's instructions need to be interpreted slightly differently to configure DNS settings properly.
What are nested subdomains?
In most cases, a subdomain is only one level deep. That is, the site domain.com may have a subdomain app.domain.com. However, it is possible that a site could use nested subdomains (i.e. multiple subdomains) in its domain configuration. For example, app.sales.domain.com has two nested subdomains (app & sales).
Interpreting Glide's Custom Domain Wizard
Since subdomains are more often one level deep, the information provided by the Custom Domain Wizard assumes this and needs to be modified when configuring the DNS settings.
Step #1
Open the Custom Domain Wizard by clicking Share->Domain->Configure in your app.
Enter a custom domain like
app.sales.domain.com.
Step #2
The Custom Domain Wizard provides TXT and CNAME records to be applied to the domain's DNS settings. Instead of using the HOST values provided in the Wizard as is, update them as described below:
The Wizard provides these HOST values
TXT: _glideauthid.app.sales
CNAME: app.sales
The correct HOST values to use
TXT: _glideauthid.app
CNAME: app
For more information about configuring Custom Domains go here.