D’Oro, a Thai coffee brand with over 20 years in the market, strengthened its position through a major rebrand in 2017 under the concept of an ‘Everyday Coffee Shop.’ Despite this, at the time of this study the brand still lacked a dedicated mobile application, relying instead on a website for point collection and paper coupons for discounts. This limitation reduced convenience, as customers could miss promotions and needed multiple steps to check order status. To address this gap, we designed a mobile application using the Product–Market Fit framework and iterative usability testing. User interviews and prototype evaluations revealed positive feedback, particularly on the simplicity of the user interface, minimal effort required for interaction, and overall usefulness in meeting customer needs. These findings suggest that a user-centered mobile application can enhance convenience, streamline service, and strengthen customer engagement.