The likelihood of a system to achieve polariton condensation depends on the efficiency with which polaritons accumulate at the lowest energy and momentum state ��𝑘𝑘 ∥ ���⃗ � = 0� and reach a critical density, where their de Broglie wavelength exceeds the average interparticle spacing . Hence, the accumulation of polaritons at �𝑘𝑘 ∥ ���⃗ � = 0 is fundamental for the formation of a condensate. In general, the relaxation of polaritons from higher to lower energy states along the polariton dispersion is mediated by many-body processes like parametric scattering and polaritonphonon scattering . However, recent research in the mechanisms by which exciton-polaritons exchange energy and momentum in 2D perovskite systems, has shown evidence of a strong polariton bottleneck that hinders population relaxation to smaller �𝑘𝑘 ∥ ���⃗ � 30 . Such a bottleneck has been shown to disappear at low temperatures (below 60 K) , where the emission spectrum of excitons in 2D perovskites becomes more defined . This observation demonstrates that the polariton relaxation mechanisms inevitably involve the ensemble of excitonic states that remain uncoupled or weakly coupled to light, referred to as the exciton reservoir.