Why am I getting the ORA-02019 error?

When you create a database link, you use the following command:

CREATE DATABASE LINK link_name CONNECT TO username IDENTIFIED BY password USING 'tns_entry';

In the above, the USING clause specifies a TNS entry in your TNSNAMES.ORA configuration file. So you have to update your config file. The ORA-2019 error is indicating that the tns entry is not found in this file. And database links always look for the tnsnames.ora config file in the ORACLE_HOME/network/admin directory. So make sure the file exists in this entry and the file is updated.