How to get BAPI return messages of user-exit message?

Hi ALL.

I have a Zprogram using BAPI 'BAPI_SALESORDER_CREATEFROMDAT2'.

and, I coded SD user-exit (FORM USEREXIT_SAVE_DOCUMENT_PREPARE (MV45AFZZ))

user-exit code is below:

-

FORM USEREXIT_SAVE_DOCUMENT_PREPARE.

　...

MESSAGE W0001(ZSD).

　...

ENDFORM.

-

I'd like to get message of user-exit message from BAPI return,

but I can't get that.

I cna get only SAP standard messages from BAPI return.

If you know how to do, let me know please.

Regards.

Rie.