Request for payment (7)
I believe the answer is:
invoice
'request for payment' is the definition.
(an invoice is sent to request payment)
This is all the clue.
(Other definitions for invoice that I've seen before include "Document detailing costs - ready to sing (7;2,5)" , "Statement of money to be paid" , "Statement for goods" , "Pollen holder" , "Give account" .)