Write the settlement down and get it signed while it is fresh

A number agreed across a table and never documented unravels the moment someone's manager questions it. When the account is agreed, record it plainly, state what it settles and what if anything it leaves open, and get it signed by people who can bind both sides before enthusiasm cools. The signed account releases the last of the money and closes the job; an unsigned understanding is just a meeting everyone remembers differently a month later.