Need to copy Data in Flexfield from PR to PO flexfield

Hi,

I create trigger to copy insert data from PR flexfield to PO flexfield when use auto create function

following this statement

CREATE OR REPLACE TRIGGER "APPS"."UPDATE_FLEXFIELD_PO" AFTER

  INSERT OR UPDATE ON PO.PO_HEADERS_ALL FOR EACH Row

  DECLARE

    V_PO_REQ_ID NUMBER;

    V_COUNT_PO_REQ_ID number;

    V_SHIP_TO_LOCATION VARCHAR2(240);

  BEGIN

    select REQ_DISTRIBUTION_ID,count(REQ_DISTRIBUTION_ID)

    into V_PO_REQ_ID,V_COUNT_PO_REQ_ID

    from po_distributions_all

    where po_header_id = :New.PO_HEADER_ID

    group by REQ_DISTRIBUTION_ID;

    IF(:New.ATTRIBUTE4 IS NULL and V_COUNT_PO_REQ_ID = 1) THEN