Payment initiated before ceiling verification (5)
I believe the answer is:
proof
'verification' is the definition.
(I've seen this before)
'payment initiated before ceiling' is the wordplay.
'initiated' suggests taking the first letters.
'before' is a charade indicator (letters next to each other).
'ceiling' becomes 'roof' (I can't justify this - if you can you should believe this answer much more).
The first letter of 'payment' is 'p'.
'p'+'roof'='PROOF'
Can you help me to learn more?
(Other definitions for proof that I've seen before include "mathematical work" , "Conclusive demonstration" , "paper for correcting" , "whisky's strength?" , "Exposition ending QED?" .)