Settle in advance (6)
I believe the answer is:
prepay
'settle in advance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for prepay that I've seen before include "Settle in advance" , "Give money (for goods) in advance" , "Remit for something before receiving it" , "Offer retainer" , "stump up ahead" .)