This paper analyzes reverse factoring in e-commerce, which is currently receiving increasing attention. As Internet technology advances during the Fourth Industrial Revolution, the e-commerce market is also growing. However, e-commerce retailers cannot keep up with the growth of the market, due to capital constraints. Supply chain finance can offer a solution to the capital constraints of e-commerce retailers. In particular, reverse factoring, a kind of supply chain finance, is a service that exchanges accounts receivable for discounted cash. It can ease the capital constraints of e-commerce retailers. Recently, peer-to-peer (P2P) lending platforms have begun to offer reverse factoring services to fill gaps in the provision of traditional financial institutions, such as banks. Supplying these reverse factoring services at a relatively low discount rate is conducive to the growth of e-commerce retailers. Therefore, we compare the discount rate of reverse factoring services according to whether the bank or the P2P platform provides the service. The existing literature on supply chain finance focuses on exploring whether retailers use supply chain finance. However, this paper compares the types of service provider used. Therefore, the models used in previous discussions are not directly applicable to the analysis in this paper. We extend the newsvendor model by reflecting the characteristics of P2P lending in our supply chain financial service analysis. We construct a demand function for retailers utilizing the newsvendor model. We also construct a supply function for each financer. We focus on the reverse auction system to explain the characteristics of P2P lending. A reverse auction is the opposite of a general auction. In the former, which many sellers compete in offering a price to a single consumer buying a product. In P2P lending, the P2P platform presents the target amount and rate of return for each loan. In this process, the platform sets the rate of return to the level at which the target amount can be raised, considering the competition among the investors. Therefore, P2P lending takes the form of a reverse auction. We consider the reverse auction form when constructing the supply of the P2P platform. This paper diverges from previous research in analyzing the demand for and supply of reverse factoring to calculate an equilibrium. The analysis reveals that the financer that can provide retailers with a low discount rate depends on market conditions: the situation in the sales market, the retailer's preference for liquidity, and the retailer's estimation of the credit risk of the e-commerce platform. The reverse factoring supply is divided into supply by the bank and supply by the P2P platform. Factors affecting the supply by the bank are the rate of return that the bank can obtain from an alternative investment option and the estimated credit risk of the e-commerce platform. Lastly, the risk aversion of P2P investors and the estimated credit risk of the e-commerce platform affect the supply by the P2P platform. We present policy implications based on these analyses. Given that P2P financing is a type of alternative financing, it is expected to offer a reverse factoring service to e-commerce retailers at a low discount rate. However, contrary to expectations, banks are currently offering services at a lower discount rate than P2P platforms are. This seems to be due to the inherent information asymmetry in the P2P lending market, which leads P2P investors to overestimate the credit risk of e-commerce platforms. This plays a key role in reducing the supply of reverse factoring through P2P platforms. If the bank's discount rate is rigid, the discount rate of the P2P platform must be reduced to reduce the burden on small e-commerce retailers. Therefore, policy discussions on ways of boosting P2P lending should be carried out. It is also essential to mitigate information asymmetry in the P2P lending market.