  Recently the observation of a new pentaquark state, the hidden-charmed
strange $P_{cs}(4459)^0$, was reported by the LHCb Collaboration. The
spin-parity quantum numbers of this state were not determined as a result of
insufficient statistics. To shed light on its quantum numbers, we investigate
its decay, $P_{cs}(4459)^0 \rightarrow J/\psi \Lambda $, the mode that this
state has been observed, within the QCD sum rule framework. We obtain the width
of this decay assigning the spin-parity quantum numbers of $P_{cs}(4459)^0$
state as $J^P=\frac{1}{2}^-$ and its substructure as diquark-diquark-antiquark.
To this end, we first calculate the strong coupling constants defining the
considered decay and then use them in the width calculations. The obtained
width is consistent with the experimental observation, confirming the quantum
numbers $J^P=\frac{1}{2}^-$ and compact pentaquark nature for $P_{cs}(4459)^0$
state.
