SilkPuppets

Hi, i'm interesting on using Spriter to my proyect. Now i don't have money to buy de pro version but a would like make a demo with the Free version. If the proyect make me win money, i have to pay to you for the use of your software?. I would like buy the pro Version but I don't know if i will get some revenue with this proyect. my question is : at some point have to pay spriter developers to use the free version of Software?. Sorry for my english And thanks for Help me!.