The antonyms for the phrase "became valid" are numerous, as there are many words that can be used to express the opposite of this statement. Some of the most common antonyms include: invalid, void, null, false, counterfeit, and fake. Each of these words is used to describe something that is not legitimate or authentic, and therefore cannot be considered valid. While there are many other possible antonyms for "became valid," these words all share the common characteristic of indicating that something is not true or real, and thus lacks the necessary authority or legal status.