Wanted to conceal advance payment (4)
I believe the answer is:
ante
'advance payment' is the definition.
(I've seen this in another clue)
'wanted to conceal' is the wordplay.
'to conceal' indicates a hidden word.
'ANTE' is hidden in the letters of 'wanted'.
(Other definitions for ante that I've seen before include "Player's stake in poker - a ten? (anag)" , "Money put at risk" , "Pay" , "Betting stake" , "'Behind, before (4)'" .)