What do you mean, the requirement of contract?

Since all states hold that receiving spousal support is a personal right – that is, it is essentially a "possession" – the recipient can also waive this right. The most common way of doing this is by a contract commonly called a "prenuptial" or "premarital agreement." Another contract that can waive or modify this right is the "separation agreement or settlement agreement"

If the underlying contract is legal and binding, the waiver of the spousal support will be legal and binding on all parties, unless the waiver would cause impoverishment or be absolutely inadequate due to a severe change in financial circumstances. Once a spouse waives the right to spousal support in a legal and binding contract it is very difficult, if not impossible to ever reverse that decision, especially when the final order is based upon a lump sum settlement in lieu of spousal support.