We consider the Drury--Arveson space on the Siegel upper half-space, which is an unbounded realization of the unit ball, and prove a von Neumann type inequality which involves what we call a Siegel-dissipative vector of operators $(A_1,\ldots, A_{d+1})$. This is a joint work with N. Arcozzi, N. Chalmoukis, M. Peloso and M. Salvatori.