SQL & PL/SQL

Oracle Version 19c.

I've compressed the BLOB data and I want to uncompress it and update it CLOB in column. However it's throwing an error

"[Error] Execution (1: 1): ORA-06502: PL/SQL: numeric or value error
ORA-06512: at line 28" due to utl_raw.cast_to_varchar2.

T1 and T2 are the same structure and column objectid being PK. How to over come this error

   create table t1 (objectid integer primary key, CPAYLOAD nclob);
var x nclob;
begin
           :x := DBMS_RANDOM.string('L',TRUNC(DBMS_RANDOM.value(10,21)));
           loop
           --:x := DBMS_RANDOM.string('L',TRUNC(DBMS_RANDOM.value(10,21)));
                   exit when dbms_lob.getlength(:x) > 14000000;
                   :x := :x || DBMS_RANDOM.string('L',TRUNC(DBMS_RANDOM.value(10,21)));
           end loop;
   end;
   /
  
    begin
          insert into t1 values (620828,:x);
commit;
   end;
   /
   
declare
   src_lob        CLOB;
   G_CLOB clob;
   pos            INTEGER := 1;
   buf            VARCHAR2(32767);
   v_len           INTEGER := 4000;
   v_blob   blob := null;
   G_BLOB   BLOB ;
   V_SQL           varchar( 4000 );
BEGIN
   SELECT CPAYLOAD INTO src_lob FROM t1 where objectid = 620828;
  -- dbms_lob.createtemporary(src_lob, true);
    for L_I IN 1..ceil(dbms_lob.getlength( src_lob ) / v_len ) loop
   buf := UTL_RAW.CAST_TO_RAW(DBMS_LOB.SUBSTR(src_lob, v_len, pos));    
   V_BLOB := hextoraw( buf );
   if nvl( dbms_lob.getlength( V_BLOB ), 0 ) > 0 then
           if nvl( dbms_lob.getlength( G_BLOB ), 0 ) = 0 then 
               G_BLOB := utl_compress.lz_compress(V_BLOB);               
           else
               DBMS_LOB.APPEND( G_BLOB, V_BLOB );
           end if;
       end if;  
   pos := pos + v_len; 
   end loop;  
   --  dbms_xslprocessor.clob2file(clobfromblob ( G_BLOB ), 'EXPORT_DIR', '620828.sql');  
   V_SQL := 'update t2 SET DPAYLOAD= :1 where objectid = 620828';
  G_CLOB := utl_raw.cast_to_varchar2(utl_compress.lz_uncompress(rawtohex(G_BLOB)));    
   execute immediate V_SQL using G_CLOB;
END;
/