A Kannappan-sine addition law on semigroups

Let $S$ be a semigroup and $z_0$ a fixed element in $S\mathrm{.}$ We determine the complex-valued solutions of the following Kannappan-sine addition law $f(xy{z}_0)=f(x)g(y)+f(y)g(x),x,y\in S\mathrm{.}$