OEM 12c: ORA-28001: the password has expired The Connect Descriptor was (DESCRIPTION=(ADDRESS_LIST = (ADDRESS=(PROTOCOL=tcp)(HOST=)(PORT=)))(CONNECT_DATA=(SID=)(SERVER=DEDICATED)))

This error occurred on DB home page in OEM 12c.
ORA-28001: the password has expired The Connect Descriptor was (DESCRIPTION=(ADDRESS_LIST = (ADDRESS=(PROTOCOL=tcp)(HOST=<host>)(PORT=<port>)))(CONNECT_DATA=(SID=<sid>)(SERVER=DEDICATED)))

Cause:

The cause of this issue is monitoring user "DBSNMP" password expired.

select username, account_status from dba_users where username='DBSNMP';

Solution:

To resolve this issue we need to reset the password and unlock the user account using the below steps.

select 'alter user "'||d.username||'" identified by values '''||u.password||''';' from dba_users d, sys.user$ u where d.username = upper('DBSNMP') andu.user# = d.user_id;

'ALTERUSER"'||D.USERNAME||'"IDENTIFIEDBYVALUES'''||U.PASSWORD||''';'
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alter user "DBSNMP" identified by values '31B5G2AQ92890956';

SQL> alter user "DBSNMP" identified by values '31B5G2AQ92890956';

Note: If you want to keep the old password then you no need to do any changes in OEM but if you want to update the new password then follow the below steps in OEM.
1.      Click Targets->Databases.
2.      Select radio button for Database Instance Name and then Click Configure
3.      Change the Monitor Password, Click Next and Submit