Oracle : RMAN-06004: ORACLE error from recovery catalog database: RMAN-20001: target database not found in recovery catalog

The backups were failing with below error after a DB refresh was done

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of show command at 02/26/2019 18:31:13
RMAN-06004: ORACLE error from recovery catalog database: RMAN-20001: target database not found in recovery catalog

Fix : 

We had to register the database by connecting to the catalog

$ rman target /

Recovery Manager: Release 11.2.0.4.0 - Production on Wed Feb 27 14:58:42 2019

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connected to target database: ABSPD2 (DBID=3485384910)

RMAN> connect catalog rman_s2rom1d2/Apr_of_2016@p1nbu1d5.db.att.com;

connected to recovery catalog database

RMAN> register database;

database registered in recovery catalog

starting full resync of recovery catalog

full resync complete

This fixed the issue and the backups started running again.