Requiring payment, they make trouble for a blockhead (5)
I believe the answer is:
bills
'requiring payment they' is the definition.
The definition suggests an adverb but the answer is not.
'trouble for a blockhead' is the wordplay.
'trouble' becomes 'ills' (I can't explain this - if you can you should give a lot more credence to this answer).
'for' says to put letters next to each other (I've seen this in other clues).
'a blockhead' becomes 'b' (head letter of 'block').
'ills' after 'b' is 'BILLS'.
'make' is the link.
Can you help me to learn more?
(Other definitions for bills that I've seen before include "Invoices" , "Draft laws" , "Beaks" .)