STEPS TO REPRODUCE
1. Open the Library Administration Control Panel (:/MicroStrategyLibrary/admin).
2. Open the Library Web Server tab.
3. Add http://test.testing.testnet:8080/MicroStrategy/servlet/mstrWeb (Strategy Web URL) to the Link: field under Strategy Web.

CAUSE
The reason for action to fail is the fact that the HTTP common URLValidator uses a predefined set of domains that it validates against - if own/custom domain name has been defined it does not validate it properly (top level domain is unacceptable for the validator).
WORKAROUND
Possible workaround is to change the parameter directly in the configOverride.properties file (services.microStrategyWeb.baseURL).
ACTION
The issue has been fixed in version 11.0.
KB441666