What's "come again" mean? Do people say this commonly?

Native speaker’s answer
Rebecca
Yes, "come again" is an informal way of saying "what did you say?" or "can you repeat that?" You can use it in casual situations when you are unclear about something, or someone has said something surprising and you want to confirm again. Ex: A: I'm getting married. B: Congrats! Wait, come again!? Ex: Come again? Say that one more time.