Crazy money? It's on credit! (8)
I believe the answer is:
crackers
'crazy' is the definition.
(I've seen this before)
'money? it's on credit' is the wordplay.
'money?' becomes 'ackers' (I am not sure about this - if you are sure you should believe this answer much more).
'it's on' is a charade indicator (letters next to each other) (some letters go on the end of others).
'credit' becomes 'cr'.
'ackers' after 'cr' is 'CRACKERS'.
Can you help me to learn more?
(Other definitions for crackers that I've seen before include "Not being sensible" , "Insane" , "Christmas items" , "Biscuits; fireworks" , "Thin biscuits for cheese" .)