What are unambiguous examples of a kiddushin that is a mekach taos, and thus the marriage is invalid?
The classical example, I think, would be if the kallah was not a besula, while the choson wasn’t aware of that fact. (Her kesuba must be for a non-besula, if that is the case.) If the choson first becomes aware of it on the night after the chasuna, he can go to beis din to nullify her kesuba. How soon after becoming aware must he notify beis din?