I also came to a solution very similar to the sibling comment here. I'd love to see why this doesn't work server-side but does work on my machine. What other tests are you running aside from checking each decrement is correct?
I'll tell you what's wrong with your code.
func below(n uint64, to chan uint64) {
for ; n >= 0; n-- {
var t = n - 1
to <- n
}
close(to)
}