Cause:
Silly ! Connection string and password should be placed inside quotes
SQL> create database link dblink_prod_qa connect to test identified by password using orcl19x; create database link dblink_prod_qa connect to test identified by password using orcl19x * ERROR at line 1: ORA-02010: missing host connect string
Solution:
SQL> create database link dblink_prod_qa connect to test identified by "password" using 'orcl19x'; Database link created.