slot sim card zenfone 2

I have ZenFone 2. awet slot 777 When I traveled to Taiwan, I used the sim card from TaiwanStar, it worked fine. awet slot 777 But when I returned to USA, I replaced it by the original sim card, and it cannot be detected I have experimented by swapping the sim cards in two slots, and trying one sim card in only one slot, ect And it works now