This is because the standby is open read-only and cannot update any tables.
When a user's account has to be locked on the standby database, it is locked only in memory there.

 

Solution :

1-

A privileged user (sysdba, the database administrator) must logon to the standby and unlock the account there.
A message ORA-28015 "Account unlocked, but the database is open for read-only access" confirms that the account is now unlocked in the standby database.
From then on, the user can logon to the standby database without getting any error.
 
SQL>alter user dbsnmp account locked;
SQL>alter user dbsnmp account unlock;

 

 

2-
Check the DB Target in EM Grid Console monitoring credentials are correct:
Navigation path:
Targets > Databases > Select the Database form the radio button > Configure > Test connection

 

 

3-
 
SQL>ALTER PROFILE new_profile 
   LIMIT PASSWORD_LIFE_TIME UNLIMITED 
   PASSWORD_REUSE_MAX UNLIMITED;
SQL>ALTER USER dbsnmp  
    PROFILE new_profile;