We present an ongoing search for new physics in proton-proton collisions at centre-of-mass energy of 13 TeV, targeting supersymmetry models with gauge-mediated supersymmetry breaking. We focus on events with a photon, an electron or a muon, and significant missing transverse momentum ($\textrm{p}_\textrm{T}^{\textrm{miss}}$), using a dataset of 137 $\text{fb}^{-1}$ collected with the CMS detector. We discuss the standard model backgrounds, event selection, and background estimation techniques in the control region to extrapolate to the signal region.