A payment for a coral island (5)
I believe the answer is:
atoll
'coral island' is the definition.
(I've seen this in another clue)
'a payment for a' is the wordplay.
'a payment' becomes 'toll' (I can't justify this - if you can you should give a lot more credence to this answer).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'toll' after 'a' is 'ATOLL'.
Can you help me to learn more?
(Other definitions for atoll that I've seen before include "Allot (anag.)" , "tropical island" , "Key" , "land threatened by rising sea levels" , "Ring-shaped coral island" .)