I recently had to reinstall the 19c database and chose not to configure a new listener since I already had an 11g listener set up. Everything was fine until I attempted to set up APEX again. The APEX installation went well, but when I tried to set up ORDS, I began encountering the following errors..

Connecting to database user: system url: jdbc:oracle:thin:@//localhost:1521/orcl
Failed to connect to user: system url: jdbc:oracle:thin:@//localhost:1521/orcl
Listener refused the connection with the following error:
ORA-12518, TNS:listener could not hand off client connection
  (CONNECTION_ID=GUdr3KiAROGLcH8vxlpaMg==)
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12518, TNS:listener could not hand off client connection
  (CONNECTION_ID=GUdr3KiAROGLcH8vxlpaMg==)

The situation seemed dire. Oracle support articles primarily addressed process deficiencies and the reconfiguration of 11g listeners for 19c database services, but these methods were ineffective for me this time. After some research, I stumbled upon a post detailing Oracle Net Services versions 9.2.0.5 to 10.2.0.1, notorious for ORA-12518 errors.

Consequently, I eliminated all 19c references from the 11g listener services and established a new 19c listener service. That turned out to be the solution. It appears that the jdbc thin clients utilized by the latest ORDS versions are incompatible with 11g net services, according to my tests. If this resolves your issue, please inform us in the comments!

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