I redeem vouchers at Kansai airport area before crossing to the Nankai train station area. You have to cross to the building on the front side of the building where you came I think it is easier for you to buy rapit train tickets directly in front of the Nankai station, which is easier and more time efficient, there is no passenger line in April 2018. Every 30 minutes the train departs. I was back and forth from the front of the train station back to the building where I arrived, because the voucher was refused and had to be exchanged for the building where I arrived. Spending time and energy because it is quite far away