Register 12c database with 19c Catalog db and rman client

Hi Community,

In order to register a 12c db target with a 19c catalog and client db, do we register it via the 12c server's rman prompt (a) or at the 19c server's rman prompt (b)?

(a)

@12c server db: rman catalog=rmancat/*******@ora19cDB target=sys/******@ora12cDB 

OR

(b)

@19c rman db: rman catalog=rmancat/*******@ora19cDB target=sys/******@ora12cDB 

We have;

Recovery cat. version 19.03.00.00.00

RMAN client version 19.3.0.0.0

Recovery db version 19.3.0.0.0

Target db Release 12.1.0.1.0

Thank you for you time.

Best Regards, Donald