superconductors with the $EPI-FSP$ pairing *the isotope effect should be small* in leading order, i.e. $\alpha\ll1/2$ [@Kulic-PhysRep]-[@Dan-Dol-Kul-Oud] - see discussion in the following. This result is contrary to the case of the isotropic $EPI$ theory in standard metallic superconductors, where $\alpha$ is maximal, $\alpha=1/2$ (for $\mu^{\ast}=0$). We point out, that the $EPI-FSP$ pairing mechanism in strongly correlated systems is rather strange in comparison with the corresponding one in standard metals with good electronic screening, where the large transfer momenta dominate and the pairing interaction is, therefore, short-range. As a result, an important consequence of the $EPI-FSP$ pairing mechanism in case of $HTSC$-cuprates is that $T_{c}$ in the $d$-wave channel is of the same order as in the $s$-wave one. Since the residual repulsion is larger in the $s$- than in the $d$-channel ($\mu_{d}^{\ast}\ll\mu_{s}^{\ast}$) this result opens a door for $d$-wave pairing in $HTSC$-cuprates, in spite of the fact of the $EPI$ dominance [@Kulic-Zeyher1-2]-[@Kulic-PhysRep].

In the following, we study the superconductivity in $1ML$ $FeSe/SrTiO_{3}$ (and $1ML$ $FeSe/TiO_{2}$ [@Rebec-FeSe-TiO2]) in the framework of a semi-microscopic model of $EPI$ first proposed in seminal papers [@Lee-Interfacial-supplement]-[@Johnston1-2]. Namely, due to oxygen vacancies: $(i)$ an electronic doping of the $FeSe$ monolayer is realized, which gives rise 