Left panel: fit of the inclusive ee yield in the 10% most central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV as a function of DCA$_{\rm ee}$ in the mass range $1.2 < m_{\rm ee} < 2.6$ GeV/$c^2$. Right panel: corresponding $\chi^{2}$ as a function of the two fit parameters, i.e. the ratio of the yield of \ee pairs originating from a prompt source or from open-charm hadron decays to the measured ee yield. See text for more details.