It sounds to me like what you’re asking for is a way to generate something you can send to a supplier saying “during this month I paid you £X on date A for invoice N, £Y on date B for invoices M and P, …”
As far as I know you can’t easily do this. You can generate the remittance advice slip as @QFMathew describes above for one single payment showing the supplier reference numbers of all the purchases it was attributed to, but not for all payments in a particular date range. You can get a list of payments made to a particular supplier via “purchases → view payments” and use the advanced search options to filter by supplier and by date, but that view only shows you the internal QuickFile reference numbers for the purchases, not the supplier’s reference.
