ORA-12505, TNS:listener does not currently know of SID given in connect descriptor

This error message indicates that the Oracle listener service is not aware of the SID (System Identifier) specified in the connection descriptor. This can happen due to several reasons, including:

1. The SID specified in the connection descriptor is incorrect or misspelled.
2. The listener service is not running or is not configured to listen for the specified SID.
3. The listener service is running on a different machine than the database server, and the connection descriptor is pointing to the wrong IP address or hostname.

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

1. Verify that the SID specified in the connection descriptor is correct and matches the SID of the database instance.
2. Verify that the listener service is running and listening for the specified SID. You can check this by running the command "lsnrctl status" on the database server.
3. If the listener service is running on a different machine, make sure that the connection descriptor is pointing to the correct IP address or hostname.

If none of these steps resolve the issue, you may need to consult the Oracle documentation or contact Oracle support for further assistance.