Long Text for all items of payment document generated by F110

Hi Experts,

Please tell me any user exit/BADI or FM which is being triggered while payment run using F110 and in which posting document number is available.

I want to create Long Text for every line item of payment docuement. Long text passed is combination of Vendor Number + References(BKPF-BELNR) for each line item.

I unable to find any exit where payment document is available.

Thanks.

Regards

Abhijit