Can I sell in an exhibition in Poland without a cashier machine?

I have an EU company and we will participate in an exhibition in Warszawa. We want to sell our products during the exhibition. Do i need a registered cashier machine? E.g. In Sweden, there is no need for an EU company to have a cashier machine (if you sell only for a limited time, like an exhibition).

Unfortunately, Polish law is designed so that you have a cash register when it comes to retail customers. A better solution is to find a partner who will be at this time to sell your products.