Poet relieved of diamonds getting payment in advance (4)
I believe the answer is:
ante
'payment in advance' is the definition.
(stake in a card game)
'poet relieved of diamonds' is the wordplay.
'poet' becomes 'dante' (I've seen this before).
'relieved of' indicates named letters should be taken away.
'diamonds' becomes 'd' (abbreviation in bridge say).
'dante' with 'd' taken away is 'ANTE'.
'getting' is the link.
(Other definitions for ante that I've seen before include "Money for poker" , "not post" , "Money put at risk" , "A neat sort of prefix" , "Stake, bet" .)