Free in FOSS means as in freedom, not free as in beer. You can demand pay for foss software. You don't have to distribute it for free. The only requirement is that you provide source code if asked for and the other person can also you can modify it and redistribute it (for a price or free) if he wants.
I'm quite out of the loop with sync for lemmy, and frankly don't give a shit. Just please don't spread disinformatiin on what foss is.
GPL and it's derivatives are ones of the most zealous of them, yet they allow you to sell the software. FOSS doesn't require you to give away software for free and it's a common misconception. Apache for example also allows you to sell the software.