The most common and most likely answer to this crossword clue is the 8 letter word DEADBEAT
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More clues leading to the result DEADBEAT
Buddy explains!

The straight part
We know that "Nonpayer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nonpayer = deadbeat.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DEADBEAT mean?
DEADBEAT noun- A lazy and/or irresponsible person who is often unemployed, often depending upon wealthy or otherwise financially independent people for support.
- A person who defaults on debts.
- (of an instrument) having a damped needle that stops without oscillation
- Defaulting on one's debts
- Defeated or exhausted
- Lazy or irresponsible
- Dead tired