Are you out of the woods if you pay a lump sum child support? If not, in what case can you still be asked to pay more money to support your child? Let's assume that the country is the United States and the couple lives in California.
I am not aware of any U.S. state that allows amounts owed for future child support to be paid in a lump sum that cannot be modified in the future if there is a change in circumstances (e.g. increased or deceased incomes of the parties, or changes in parenting time).
There may be an exception for very high income families where the child support guidelines set under state law (but mandated by federal law), apply and the maximum guideline amount is paid in a lump sum.
Lump sum alimony (a.k.a. spousal maintenance), however, may be paid in a lump sum, as may child support for periods that have taken place in the past, whether or not they are past due.