SX20 is in Singapore,cucm core is in Beijing.
I have put rootCA cert in the SX20 already.
Set NTP and DNS(local) already.
Username and password was imported from LDAP.
SX20 can not registered.

You can try cisco Collab Edge Validator in Cisco Collaboration Solution Analyzer
https://cway.cisco.com/tools/CollaborationSolutionsAnalyzer/