I got error while running tuning advisory

I created the following SP  for  SQL Tuning Advisory pacakge .

CREATE OR REPLACE procedure MASTER_DEV_HEAD.func_sql_tune( sqltext_var varchar2,sql_tune_result varchar2,v_username varchar2)
as
task_name_var VARCHAR2(30):= 'test1';
BEGIN
task_name_var := DBMS_SQLTUNE.CREATE_TUNING_TASK(
sql_text => sqltext_var,
user_name => v_username,
scope => 'COMPREHENSIVE',
time_limit => 60,
task_name => task_name_var ,
description => 'This is a test tuning task on EMP table');
dbms_sqltune.Execute_tuning_task (sql_tune_result);
END;
/

I use the following code to execute the sp and here is the code

declare p_sql clob