ORA-12514: TNS:listener does not currently know of service requested in connect descriptor

Before start to create standby database by using DUPLICATE command, try to connect to  auxiliary instance:

RMAN>  connect auxiliary  sys/password@testdbsty

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-04006: error from auxiliary database: 
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor
$ sqlplus sys/password@testdbsty as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Tue Jan 15 15:18:35 2019

Copyright (c) 1982, 2013, Oracle. All rights reserved.

ERROR:
ORA-12154: TNS:could not resolve the connect identifier specified

Workaround:

Add an entry in listener.ora, and then reload listener to make it effective:

SID_LIST_LISTENER =
(SID_LIST =
   (SID_DESC =
      (GLOBAL_DBNAME = TESTDBSTY)
      (SID_NAME = TESTDBSTY)
      (ORACLE_HOME = /u01/app/oracle/product/11.2.0/dbhome_1)
  )
..
.
}

$lsnrctl status
Services Summary...
Service "TESTDBSTY" has 2 instance(s).
  Instance "TESTDBSTY", status UNKNOWN, has 1 handler(s) for this service...
  Instance "TESTDBSTY", status BLOCKED, has 1 handler(s) for this service...
...
.
.