Ensure that your account has the database administrator (DBA) role, Database Monitoring is enabled in the instance, and your user name is uppercase at sign-in.

To access the Database Monitor page, you meet the following requirements:

• Your database account that has been granted a database administrator (DBA) role.
• Database Monitoring is enabled for the instance. Your intance administrator can enable this from Instance Administration or use APEX_INSTANCE_ADMIN.SET_PARAMETER to set the ALLOW_DB_MONITOR parameter value.

When all requirements are met, sign in using the database account with DBA role with an UPPERCASE user name.