The URL UMP dashboard is asking for credentials
Even when you passed(filled) the username and password on the URL.
The dashboard is not able to get to the listener DB since no connections is available.
ORA-12516, TNS:listener could not find available handler with matching protocol stack
UIM with Oracle DB
Increase the number of connections on the DB size.
ALTER SYSTEM SET PROCESSES = 500 SCOPE=SPFILE;
ALTER SYSTEM SET SESSIONS = 555 SCOPE=SPFILE; -- 1.1 * PROCESSES +5
Make sure at your DB already has configured 200, 300 or 400 this will work but If your DB has alredy 500 or above, please adjust for what you need.