We just set up Clover Flex. Tried to use it both with Cellular and Wi-Fi connections. In both cases all cards used so far are Declined with ERROR 63. These cards have been used with other devices and they do work. So we are mystified as to what it can be. We thought it was the Cellular connection not reading properly the CVV number/code. So we tried Wi-Fi but the same. So there is some reason for this but don't have any idea of what it can be.