Syncthing and SyncTrayzor are free software, and you don't need to pay a penny to use them. However, if you find them useful, please consider giving a small amount to one of the causes below.
SyncTrayzor is just the wrapper around Syncthing, which makes it look and behave like a native Windows application. The heavy lifting is being done by Syncthing.
While development is done for free by a fantastic team, running the infrastructure which lets your devices find and talk to each other costs money, as does hosting things like the website and forum. If you make use of these, I kindly ask that you consider sending a small amount towards funding Syncthing's running costs and future development. Donations are handled by the Syncthing Foundation, whose accounts are public.
If you wish to donate to me directly, I have a GitHub sponsors page. Note that I am not directly involved with Syncthing development (nor do I receive funding from them), but only SyncTrayzor development.