The zero-sum 3-flow conjecture for Steiner triple systems

A Steiner triple system ${\rm STS}(v)$ is a $2$-$(v,3,1)$ design. A zero-sum $n$-flow of a design $\mathcal{D}=(X,\mathcal{B})$ is a map

$$f:\mathcal{B}\longrightarrow \{\pm1,\ldots,\pm(n-1)\}$$

such that the sum of the values over all blocks incident with each point is zero. The zero-sum 3-flow conjecture. Every ${\rm STS}(v)$ with $v>7$ admits a zero-sum $3$-flow. This conjecture concerns the existence of bounded integer flows on the incidence structures of Steiner triple systems; the source gives no evidence of resolution.