Hilchos Ishus 6:4
Let’s say that a man told a woman that she is consecrated to him through a dinar. He gives it to her and only then stipulates that it is conditional upon her giving him 200 zuz, and if she doesn’t, then she is not consecrated to him. In such a case, the condition is immaterial because he performed the act of giving her the dinar before he made the condition. This is so even if all this transpires in a very brief span of time. Marriage is immediately effected and she need not give him anything.
Hilchos Ishus 6:5
Similarly, let’s say that a man tells a woman, “If you give me 200 zuz, you are consecrated to me through this dinar,” after which he gives it to her. Such a condition is invalid because it did not include the ramifications of not fulfilling it, i.e., that if she doesn’t give it to him, she won’t be consecrated. In this case, marriage is immediately effected and she need not give him anything.