Passing dynamic Columns to Pivot in Oracle

I am new to oracle, I am trying to pass the dynamically generated column names to pivot in oracle using the below query

DECLARE
   v_cols VARCHAR2(100);
   v_query VARCHAR2(4000);

BEGIN

    SELECT LISTAGG('''' ||product_code||'''',',') WITHIN GROUP (ORDER BY product_code) 
    INTO v_cols
    FROM (
        SELECT  DISTINCT product_code
        FROM pivot_test
        );

    v_query:='
      SELECT *
      FROM   (
              SELECT product_code,
                     quantity
              FROM   pivot_test) 
              PIVOT (sum(quantity) AS qunts 
              FOR product_code IN ('|| v_cols ||'));';

    EXECUTE IMMEDIATE v_query;
    --dbms_output.Put_line(v_cols); 
    --dbms_output.Put_line(v_query);   
END;

The column generated is 'A','B','C','D' and the query generated with dynamic column is

SELECT *
FROM   (
              SELECT 
                     product_code,
                     quantity
              FROM   pivot_test) PIVOT (sum(quantity) AS qunts FOR product_code IN ('A','B','C','D'));

Result:

When I take the above query and run it separately it is running correctly but when I use EXECUTE IMMEDIATE v_query; I get the error

  ORA-00911: invalid character
  ORA-06512: at line 20

I am not aware what is causing the problem here can any please point me what is wrong with this dynamic query execution

Value used for testing

CREATE TABLE pivot_test
  (
     id           NUMBER,
     customer_id  NUMBER,
     product_code VARCHAR2(5),
     quantity     NUMBER
  );

INSERT INTO pivot_test VALUES (1,1,'A',10);    
INSERT INTO pivot_test VALUES (2,1,'B',20);    
INSERT INTO pivot_test VALUES (3,1,'C',30);    
INSERT INTO pivot_test VALUES (4,2,'A',40);    
INSERT INTO pivot_test VALUES (5,2,'C',50);    
INSERT INTO pivot_test VALUES (6,3,'A',60);
INSERT INTO pivot_test VALUES (7,3,'B',70);
INSERT INTO pivot_test VALUES (8,3,'C',80);    
INSERT INTO pivot_test VALUES (9,3,'D',90);    
INSERT INTO pivot_test VALUES (10,4,'A',100);

COMMIT; 

Copyright Notice：Content Author:「Rajesh」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/60867255/passing-dynamic-columns-to-pivot-in-oracle