3498871 - "Could not reach test WS through specified SAP Web Dispatcher" error in SOLMAN_SETUP "Define HTTP Connectivity"

In 2.1 "Define HTTP Connectivity" page, when click on "Check URL" button of "Use SSL for Internal WS Access", the error will be displayed as below
Could not reach test WS through specified SAP Web Dispatcher: https://<SAP Web Dispatcher hostname>:<WDP HTTPS port>
Message No. CL_URLAPI_MESSAGE059

But when click on "Check URL" button of "URL (External Access)" with same SAP Web Dispatcher hostname & port, there is no issue, message like:
SAP Web Dispatcher for External Access: URL <SAP Web Dispatcher hostname>:<WDP HTTPS port> reached

As client, Solman system will establish SSL connection to SAP Web Dispatcher, in SRT_UTIL or ICM trace of Solman system, following errors can be observed:
[Thr xxxxxx] *** ERROR => SSL handshake with <SAP Web Dispatcher hostname>:<WDP HTTPS port> failed: SSSLERR_PEER_CERT_UNTRUSTED (-102)
[Thr xxxxxx] Peer's X.509 certificate (chain) validation failed (missing trust?)
[Thr xxxxxx]
[Thr xxxxxx]SapSSLSessionStartNB()==SSSLERR_PEER_CERT_UNTRUSTED
[Thr xxxxxx]   SSL:SSL_read() failed  
[Thr xxxxxx]   => "Failed to verify peer certificate. Peer not trusted."
[Thr xxxxxx]   SSL:SSL_get_state()==0x2131 "TLS read server certificate B"
[Thr xxxxxx]   SSL NI-hdl 285: local=xxx:<ICM port>  peer=xxx:<WDP HTTPS port>
[Thr xxxxxx]   acli SSL session PSE "/usr/sap/<Sloman SID>/<instance>/sec/SAPSSLX.pse" (load=xxx xx:xx:xx 2024, rcnt= 0) 

SAP Web Dispatcher

Could not reach test WS through specified SAP Web Dispatcher, Use SSL for Internal WS Access, URL (External Access), SSSLERR_PEER_CERT_UNTRUSTED , KBA , BC-CST-WDP , Web Dispatcher , SV-SMG-INS-CFG , Setup and Configuration of the Solution Manager system , BC-SEC-SSL , Secure Sockets Layer Protocol , Problem