While the mobile gift coupon market is growing, there is limited research on the fees that digital platforms charge sellers. Additionally, there have been persistent complaints that the fees set by the dominant platform are not only excessive but also discriminatory. In this study, we empirically examine the factors that influence fee determination. A simple theoretical model was developed based on the characteristics of the mobile gift coupon market and its participants, formulating a hypothesis to explain how the margin rate (sellers' willingness to pay) and the proportion of mobile gift coupon sales affect platform fees. This hypothesis was tested using survey data from 250 franchisees across 50 brands. The results showed a positive relationship between fees and a brand's operating profit rate (margin rate), moderated by the proportion of mobile gift coupon sales. Finally, we discuss how the recent fee caps could impact smaller brands.