3011015 - Calling an RPC vis DC/TRS returns: Request rejected. No host connections are defined to the requested subsystem

• When trying to call a RPC via Directconnect (DC) Transaction Router Service (TRS) the following error appears in the client application:
  
  Msg 34256, Level 11, State 0:
  Server 'xxxxxx':
  Request rejected. No host connections are defined to the requested subsystem.
  Contact the DirectCONNECT administrator.
  
  
• DC server log shows:
  
  LogClientLogin 01/08/2021 17:48:31.146877 m3xssl 8 <USER> isql Connection attempt... user: '<USER>' application: 'isql' service: '<TRS Service>'
  LogClientLogin 01/08/2021 17:48:31.147238 <TRS Service> 8 <USER> isql ...Connection successful. TDS Level [5.0], enum=[9]
  LogTRS 01/08/2021 17:48:55.537001 <TRS Service> 8 <USER> isql #34256 Request rejected. No host connections are defined to the requested subsystem. Contact the DirectCONNECT administrator.
  
  

• DirectConnect (DC) for z/OS 15.0.1

TRS, DC, sgw_addregion, sgw_addrpc, 34256, No host connections are defined to the requested subsystem , KBA , BC-SYB-MFC , Mainframe Connect (MFC) , Problem