Settle early (6)
I believe the answer is:
prepay
'settle early' 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 "stump up ahead" , "Fork out in advance of delivery" , "Settle in advance" , "Offer retainer" , "Remit for something before receiving it" .)