validators

var (
	ErrCardNumberFormat = errors.New("card number must match the format xxxx xxxx xxxx xxxx")
	ErrCVVFormat        = errors.New("card's CardCVV must be a 3-digits value")
	ErrExpDateFormat    = errors.New("card's expire date must match the format mm/yy")
	ErrExpDateInPast    = errors.New("card's expire date must not be in the past")
)