Discover there's money to be paid (5)
I believe the answer is:
learn
'discover' is the definition.
('learn' can be a synonym of 'discover')
'there's money to be paid' is the wordplay.
'there's' is a charade indicator (letters next to each other).
'money' becomes 'l' (L can mean 'pounds').
'to be paid' becomes 'earn' (I've seen this before**).
'l' put next to 'earn' is 'LEARN'.
(Other definitions for learn that I've seen before include "Gain knowledge or skill" , "Become aware of" , "be taught a lesson" , "Commit to memory" , "Study (at school?)" .)