archive log gap in physical standby database

one of the cause
ORA-12154:TNS:could not resolve the connect identifier specified

>>>alert_.log

search for GAP keyword in alertlog.

sequence=8171 thread=1;

I had to restore that on the primary side

rman target / catalog rman/rman@abc

RMAN>restore archivelog sequence=8171 thread=1;

:):):)