Check number and PO NUmber in Idoc PEXR2002

Hello Gurus,

I am having a problem with Idoc of outgoing Payment. We are Using Idoc PEXR2002 with Message type "PAYEXT" for outgoing Payment. We need the PO Number (EBELN) and Check Number (CHECT) in the IDOC. Does somebody tell me how to send the PO Number (EBELN) and Check Number (CHECT) in the Payment Idoc? Is there any User Exit available to populate Check No and PO Number? If yes what is the SAP note No ? Please update me with solution. Help will be highly appreciated

Thanks in advance