We investigate the effects of entry of financial technology (FinTech) based firms on competition in the retail payments market. With a model of two-sided market with vertical restraints, we derive the following results. When only the entry of a vertically integrated (or end-to-end service) provider is allowed, either all merchants opt for multi-homing or no entry occurs, regardless of the regulatory requirement. On the other hand, if the entry of a downstream-only (or front-end service) provider is allowed, a partial multi-homing equilibrium could emerge under certain conditions, in which the entry of an end-to-end service provider does not occur. Without regulation, however, the vertically integrated incumbent does not voluntarily provide the back-end service to the entrant in general. This suggests the need for proper regulatory measures to reach a socially desirable outcome from the new entry in the retail payments market.