Beloshapka's maximal symmetry conjecture for holomorphically nondegenerate CR-hypersurfaces

Let $M$ be a real-analytic connected holomorphically nondegenerate CR-hypersurface of CR-dimension $n$, and let $\mathfrak{s}(M)$ denote its symmetry algebra. Beloshapka's conjecture. One has

$$\dim\mathfrak{s}(M)\le n^2+4n+3,$$

with the maximal value $n^2+4n+3$ attained only if $M$ is spherical on a dense open set. This is a variant of a conjecture due to V. Beloshapka concerning the maximal possible symmetry dimension in the real-analytic holomorphically nondegenerate setting. The supplied source does not establish its resolution.