ORA-12514, TNS:listener does not currently know of service requested in connect descriptor

ORA-12514 error occurs when the listener does not know the service name that is requested in the connection descriptor. It can happen due to several reasons such as a wrong service name, incorrect configuration, or the service is not registered with the listener.

To resolve this error, you can try the following steps:

1. Check if the service name in the connection descriptor is correct.
2. Ensure that the listener is running and configured to listen to the correct port and protocol.
3. Make sure that the service is registered with the listener. You can check the listener.ora file to see if the service is listed.
4. Restart the listener and try to connect again.

If none of the above steps work, you can try to connect using the full database service name instead of the shortened service name. For example, instead of using "ORCL", use "ORCL.mydomain.com".