License #?

I went to install Flip 4 Mac on my iMac, and suddenly, I was confronted with a screen that said I've gotta provide a LICENSE NUMBER! I was unaware this was required. I assumed when I came across the "Free download," that it would just be download for free, install, and go right to watching Windows Media videos. Obviously I was mistaken. Do you give out free licenses, or do I actually have to BUY one? Thanks!