final payment vs payoff

final payment and payoff both are nouns.

Word	Noun	Adjective	Verb	Adverb
final payment	Yes	No	No	No
payoff	Yes	No	No	No

As nouns, final payment and payoff are synonyms defined as:

final payment (noun)	payoff (noun)
the final payment of a debt	a recompense for worthy acts or retribution for wrongdoing
	the final payment of a debt
	payment made to a person in a position of trust to corrupt his judgment
	the income or profit arising from such transactions as the sale of land or other property