Linking a Debit note to AP Invoices

Hi All

Thanks in adavance for your kind helps

we have enabled suppliers  for self billing and enabled for Debit memo for the returns

My query is how can i enable the system while creating RTV Returns , which invoice to debit in to? i.e

Lets say the receipted value was 100

Invoice1 created for 100

return created for 20

Debit note created for 20, but as a seperate transaction in AP

I am expecting that , as the invoice and debit notes refers to same receipt, debit notes will understand the invoices to which it is debited to.. but it is not..one draw back is hence the withholding tax applied in to the invoice is not defaulted to Debit notes..