I can’t urge you enough to do this enough. There is nothing worse for a theatre/show to have empty seats. It doesn’t look good. So producers work with companies to get people to fill out those seats on the day/in the week. It’s better for them, that your sat in the audience, potentially buying a brochure and a beer – than have an empty seat, making the show seem unsuccessful. Showfilmfirst is the big free website that offers this, but there are paid ones too which I’ve tried – but I don’t rate.