How to buy fitfi step app?

Could you please elaborate on the process of purchasing the FitFi step app? I'm interested in understanding the steps involved, from start to finish. Is there a specific platform or marketplace where I can find and buy the app? Are there any requirements or prerequisites that I need to meet before making the purchase? Additionally, is there a payment method that is preferred or accepted by the app's developers? I'd appreciate any information you can provide to help me navigate the process of acquiring the FitFi step app.