Hi, I think you need to check the follwing:
1- on the vendor proposal form click on select and select the “method of payment” of which you want to run the payment proposal
2- select also the currency if applies to your company
3- click OK
3- Back in the payment proposal form, in order the system to add all the pending invoices in one payment (check, EFT, wire, etc…), on minimum date select a future date (Dec 31 2014) because if not the system will split it according with the due date, in one payment will be put together all the over due invoices and in other one or others the other invoices depending on the due date
because you are selecting a future date all the lines in the bottom part of the window will have that future date but you can change it for the one you want in the multiple change button in the payment proposal
Practically is matter of paying with the dates or what exactly you want to pay.
I hope this helps