If you are in SQL*Plus or SQL Developer, you want to run
SQL> set define off;
before executing the SQL statement. That turns off the checking for substitution variables.
SET directives like this are instructions for the client tool (SQL*Plus or SQL Developer). They have session scope, so you would have to issue the directive every time you connect (you can put the directive in your client machine’s glogin.sql if you want to change the default to have DEFINE set to OFF). There is no risk that you would impact any other user or session in the database.