Cannot configure DataGuard on standby database

I am configuring DataGuar between primary and standby databases. I did the following:

DGMGRL> show database 'PrimaryDB';

Database - PrimaryDB

  Role:            PRIMARY
  Intended State:  TRANSPORT-ON
  Instance(s):
    PrimaryDB

Database Status:
SUCCESS

DGMGRL> show database 'StandbyDB';

Database - StandbyDB

  Role:            PHYSICAL STANDBY
  Intended State:  APPLY-ON
  Transport Lag:   (unknown)
  Apply Lag:       (unknown)
  Real Time Query: OFF
  Instance(s):
    StandbyDB

Database Status:
DGM-17016: failed to retrieve status for database "StandbyDB"
ORA-16532: Data Guard broker configuration does not exist
ORA-16625: cannot reach database "StandbyDB"

So I checked configuration:

DGMGRL> show configuration

Configuration - PrimaryDB_DG

  Protection Mode: MaxPerformance
  Databases:
    PrimaryDB  - Primary database
    StandbyDB - Physical standby database