The paper explores the possibility that the observed excess in the rare $ B^{+} \rightarrow K^{+} \nu \bar{\nu} $ decay, measured by the Belle II collaboration, is explained by a massless dark photon interacting with a dark sector. This dark photon, denoted $ \gamma_D $, mediates long-distance interactions that produce a pair of dark fermions, $ Q_i $, in the decay process. The dark fermions are not directly observed but contribute to a missing energy signature in the detector, mimicking the neutrino signature in the Standard Model (SM) prediction. The excess is attributed to the interaction of the $ B^{+} $ meson with the dark photon, which is not directly observable due to angular momentum conservation. Instead, the dark photon is virtual, leading to a three-body final state with a missing energy continuum. The scenario predicts new contributions to the neutral B meson decay $ B^{0} \rightarrow K^{*} \gamma_D $, where the emission of a real dark photon is allowed, resulting in a monochromatic missing energy signature. This decay could be tested at future experiments like LHCb. The model also predicts an excess in the decay $ B_{s}^{0} \rightarrow \phi + E_{miss} $, which could be observed at LHCb. The analysis shows that the Belle II data can be explained with perturbative values of the model parameters, and the scenario is consistent with current experimental constraints. The paper also discusses the implications of the dark photon scenario for other decays, such as $ B^{0} \rightarrow K^{*} \nu \bar{\nu} $, and how the absence of a signal in this decay constrains the number of dark fermion generations. The model is consistent with the SM predictions for other processes and provides a framework for testing the dark photon hypothesis in future experiments. The results suggest that the observed excess in $ B^{+} \rightarrow K^{+} \nu \bar{\nu} $ could be explained by a dark photon-mediated interaction, with potential observable signals in other decays. The scenario is experimentally viable, as it is only loosely constrained by the weak coupling of the dark photon to the visible sector.The paper explores the possibility that the observed excess in the rare $ B^{+} \rightarrow K^{+} \nu \bar{\nu} $ decay, measured by the Belle II collaboration, is explained by a massless dark photon interacting with a dark sector. This dark photon, denoted $ \gamma_D $, mediates long-distance interactions that produce a pair of dark fermions, $ Q_i $, in the decay process. The dark fermions are not directly observed but contribute to a missing energy signature in the detector, mimicking the neutrino signature in the Standard Model (SM) prediction. The excess is attributed to the interaction of the $ B^{+} $ meson with the dark photon, which is not directly observable due to angular momentum conservation. Instead, the dark photon is virtual, leading to a three-body final state with a missing energy continuum. The scenario predicts new contributions to the neutral B meson decay $ B^{0} \rightarrow K^{*} \gamma_D $, where the emission of a real dark photon is allowed, resulting in a monochromatic missing energy signature. This decay could be tested at future experiments like LHCb. The model also predicts an excess in the decay $ B_{s}^{0} \rightarrow \phi + E_{miss} $, which could be observed at LHCb. The analysis shows that the Belle II data can be explained with perturbative values of the model parameters, and the scenario is consistent with current experimental constraints. The paper also discusses the implications of the dark photon scenario for other decays, such as $ B^{0} \rightarrow K^{*} \nu \bar{\nu} $, and how the absence of a signal in this decay constrains the number of dark fermion generations. The model is consistent with the SM predictions for other processes and provides a framework for testing the dark photon hypothesis in future experiments. The results suggest that the observed excess in $ B^{+} \rightarrow K^{+} \nu \bar{\nu} $ could be explained by a dark photon-mediated interaction, with potential observable signals in other decays. The scenario is experimentally viable, as it is only loosely constrained by the weak coupling of the dark photon to the visible sector.