This error usually would come up on your APEX/ORDS instance if the user apex_public_user has expired. The quickest solution is to reset the password for apex_public_user and set it to a profile without any password expiration policy
1. Check user apex_public_user has expired
set lines 999 select account_status, profile from dba_users where username = 'APEX_PUBLIC_USER' ;
2. Reset the apex_public_user password
SQL> alter user apex_public_user identified by P@ssw0rd! ;
3. Go to ORDS config directory
$ cd /u01/conf/ords/conf/
4. Edit the file apex.xml which has the password stored as a hash value
/u01/conf/ords/conf:12cR2--> vim apex.xml
5. Add edit the db.password tag with the new password
<entry key=”db.password”>P@ssw0rd!</entry>
Save the file & Restart Apache Tomcat
Helpful Resources to Troubleshoot Error :
APEX 503 – Service Unavailable – And you don’t know the APEX_PUBLIC_USER Password
