Not so FIRE service

On the afternoon of 18.02.2019 at around 17:55 me and my partner went to Nandos Cresta to buy full chicken and other items. My partner was going to make payment with a gift voucher and pay the difference in cash and she advised the cashier about that. The cashier told her the voucher machine doesn't work which doesn't make sense as my understanding is that you use the same credit/debit card machine for voucher purchases (correct me if I am wrong) this is Frustrating considering we went specifically to Cresta just to make the purchase at that Nandos and wasted our time driving there. There was no notice saying the voucher machine didn't work, the cashier didn't even make an effort to try see how they can assist and does that mean if 20 ppl with vouchers had come after that, they would have been turned away because of this machine???? Very inconsiderate to yr customers Nandos!!! Did you even advice Cresta management about this problem ....This is bad customer service