Spain is not on the list of supported countries yet. It most likely has to do with the way NiteFlirt is paying their models, which is by paper check if you live outside the US. I assume that Spanish banks don't like this system, or that they don't have regulations when it comes to paper checks. You could try to make an account by using a US bank account and a US phone number. You should contact NiteFlirt support and find out what other options they suggest.