Advance needing to be paid? Keep quiet (6)
I believe the answer is:
subdue
'keep quiet' is the definition.
(if someone is subdued they are kept quiet)
'advance needing to be paid?' is the wordplay.
'advance' becomes 'sub' (I've seen this in other clues).
'needing' says to put letters next to each other.
'to be paid?' becomes 'due'.
'sub'+'due'='SUBDUE'
(Other definitions for subdue that I've seen before include "Quash" , "Overcome, bring under control" , "Force to yield, tame" , "Quell" , "Conquer" .)