how to fix Error: ORA-16664: unable to receive the result from a database

Hi,

I created one physical standby database. When I  run dataguard command, this show error. Looks like primary is good but standby has issue, can anyone have this problem before? thanks

DGMGRL> show configuration;  

Configuration - PNY02700

  Protection Mode: MaxPerformance
  Databases:
    PNY02700 - Primary database
    SNY02700 - Physical standby database
      Error: ORA-16664: unable to receive the result from a database

DGMGRL> show database "PNY02700"

Database - PNY02700

  Role:            PRIMARY
  Intended State:  TRANSPORT-ON
  Instance(s):
    PNY02701
    PNY02702
    PNY02703

Database Status:
SUCCESS

DGMGRL> show database "SNY02700"

Database - SNY02700

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