COBOL DB2 PROCEDURE

I am new to COBOL language. After I studied through the tutorials with Visual COBOL.  I tried to write my first DB2 stored procedure.

This is my environment setup:

Windows 10 Enterprise Edition.    I installed DB2 10.5 Express Edition , Visual Studio 2015 Enterprise Edition, Visual COBOL 2.3  personal edition.

I compile the following code as Library Project, output as DB2PROC.dll

       identification division.
       program-id. DB2PROC.

       environment division.
       configuration section.

       data division.
       
       linkage section.
       01 INPARAM      PIC X(20).                 
       01 OUTPARAM  PIC X(80).

       procedure division USING INPARAM
                                                      OUTPARAM.
       string INPARAM delimited by spaces  
              ' COBOL WORLD!!!'delimited by space  into OUTPARAM
           goback.
       end program DB2PROC.

I copied DB2PROC.dll into IBM\SQLLIB\FUNCTION  folder, I also copied COBOL run-time library  cblrtsm.dll in the same folder.

Then I created DB2 stored procedure:

CREATE PROCEDURE DB2PROC
(IN INPARAM CHAR(20), OUT OUTPARAM  CHAR(80))
RESULT SETS 0
MODIFIES SQL DATA
LANGUAGE COBOL
EXTERNAL NAME  'C:\Program Files\IBM\SQLLIB\FUNCTION\DB2PROC.dll'
FENCED
NOT THREADSAFE
NO DBINFO
PROGRAM TYPE SUB
PARAMETER STYLE GENERAL;

From  IBM data studio, when I call that procedure, it gives me error:

[jcc][t4][1065][12306][3.68.61] Caught java.io.CharConversionException.  See attached Throwable for details. ERRORCODE=-4220, SQLSTATE=null
Run of routine failed.
 - Roll back completed successfully.

But if I change the 2nd parameter as INOUT

CREATE PROCEDURE DB2PROC
(IN INPARAM CHAR(20), INOUT OUTPARAM  CHAR(80))

The error is gone,  I can run it successfully.  but OUTPARAM does not return anything to me.

Could someone help me to point out what is wrong with my code?

Really appreciated.