Your separation agreement has to follow certain rules to make it binding and enforceable under the law. This means your agreement is made in a way that allows the court to order you or your partner to do what the agreement says, if either of you stop following it.
If your separation agreement didn't follow these rules, you or your partner can ask the court to set aside your agreement. This means asking the court to allow you not to follow the agreement.
If this happens, you and your partner can make a new separation agreement that follows the rules or the court can decide what happens.