Restaurant Refusing To Take Gift Card In Nyc

Context: I lived in NYC for a little while. 2 years ago, my brother got me a gift card to one of my favorite restaurants there. Ended up moving out of the city for work so did not get a chance to use it then. Over the summer, I went back to that restaurant and tried to use it, but they told me that there was a problem with the machine to process gift cards. I went there again today to try and use it, but this time they told me that the card was too old because they replaced their gift card reader two months ago and it won't read it. They told me to throw out my gift card. It was $25 I think, but still, I have a feeling they are trying to prevent me from using it. I kept the gift card and intend to try it again the next time I go there. Is this legal? What should I do the next time I go there? I really am not the type to complain or anything at a restaurant but this is coming across as kind of shady.