When running a script through QSR (Quest ScriptRunner), it is not displaying dbms_output messages.
This is happening even if DBMS_Output is enabled.
QSR is not a debugging tool, and it doesn't show DBMS output unless you use SET SERVEROUTPUT ON. Even then, it will work only when executing a DB-compiled proc or package.
If the code is an anonymous block and not a DB-compiled object, there will also be no output.