Differential cross section as a function of $\it{p}_{\rm{T, KK}}^{\rm{2}}$ for exclusive ${\rm K^+K^-}$ photoproduction in Pb$-$Pb UPCs at $\sqrt{s_{\rm{NN}}}$= 5.02 TeV and $|y_{\rm{KK}}|<0.8$. The lines and boxes across the data points represent statistical and systematic uncertainties, respectively. The dashed blue line and band are the result of a fit to an exponential with the fixed slope parameter $b=428\ \pm\ 6\ ({\rm stat.})\ \pm\ 15\ ({\rm syst.})$ $({\rm GeV}/c)^{-2}$, from a previous result on $\rho^{0}$ production (see text for details). The inset shows two curves from STARlight with and without interference between the two photon directions.