I created the bill payment by: 

1. click to the AP vendor that I am paying

2. click on any opening invoices under this AP vendor that shows 'make payment'

3. remove all the bills applied to this payment and enter the amount that I am paying

4. save and record.

This way, all my invoices are open but my AP is reduced. This is wrong as I realised all the opining invoices accumulated and affects my AP aging.

Please let me know if there is a way.

Thank you