The payment is done via Stripe so you need to make an account there if you are using the component an you must get the code they offer and to add it into the configuration. The Joomla component will be free because we are going to use it for consulting in a website (invoicing is separate because our services are counted) that we are not owning but there can be written again about internet, weold wise web, software engineering and various stuff. It is not clear yet if you will grt it by request of you will be able to download it from JED directory but you can get it (download it) for free. It's named JTips.