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

Reason:-
Service name provided in log_archive_dest_2 parameter is wrong for standby;

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Solution:-
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As you see below , SERVICE_NAME in tnsentry mentioned as STDBY_DR and db_unique_name is STDBY, chaging the service_name in tnsnames.ora will resolve the issue 


1. select value from v$parameter where name='log_archive_dest_2';
value
------
service=TEST ASYNC NOAFFIRM valid_for(all_logfiles,all_roles) db_unique_name='STDBY';


2. vi tnsnames.ora

TEST =
   (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = standbyhost)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = STDBY_DR)
    )
)