Get back about demand for payment (7)
I believe the answer is:
reclaim
'get back' is the definition.
(I've seen this before)
'demand for payment' is the wordplay.
'demand' becomes 'claim' (claiming is a kind of demanding).
'for' means one lot of letters go next to another (I've seen this in other clues).
'payment' becomes 're' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'claim' put after 're' is 'RECLAIM'.
'about' acts as a link.
Can you help me to learn more?
(Other definitions for reclaim that I've seen before include "Recover (materials/land) for subsequent use" , "I'm Clare (anag)" , "Make (land) available for use" , "Win back" , "Retrieve, recover" .)