Unfortunately, neither method works.
When viewed from the entity, the error message is:
{myorg}.crm0.dynamics.com’s server IP address could not be found.
When viewed from within the solution customization's iFrame, the error message is:
This site can’t be reached
Check if there is a typo in {myorg}.crm0.dynamics.com.
If spelling is correct, try running Windows Network Diagnostics.
DNS_PROBE_FINISHED_NXDOMAIN