ERROR: Checking sync on Primary and Standby... Failed

Solution:-

Step 1: - Take backup of missing log sequence

RMAN> backup format '/home/oracle/arch_%s_%p_%t.bkp'
(ARCHIVELOG FROM SEQUENCE 8201 UNTIL SEQUENCE 8203 THREAD 2);

Step 2:- scp backup set to standby server

Step 3:- Catalog specific backup piece with standby.

CATALOG BACKUPPIECE '/home/oracle/arch_%s_%p_%t.bkp';

Step 4:- restore archive log on standby server

RMAN> restore archivelog sequence 225 thread 1;