Not to be paid in improper fashion (5)
I believe the answer is:
undue
'not to be paid' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for undue that I've seen before include "Not warranted" , "Improper" , "Excessive, disproportionate" , "Unwarranted, inordinate" , "too much" .)