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;