First, you need to ensure that your remote server's listener is up and running, and listening for the database you want to connect to. Then, you have to make sure that your TNS alias, defined in your local TNSNAMES.ORA is pointing to the correct server and the correct Oracle Listener port, and the correct database SID. The ORA-12203 error indicates that the TNS alias information does not match the information on the server.
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