We designed and implemented a gamified eHealth application for youth mental healthcare, to study how game design techniques could be applied within this context. This resulted in the design of a gamified mobile application aimed at supporting therapeutic goal setting: the ReadySetGoals game. The design process itself involved four key stages: (1) Identifying the transfer effect to be aimed-for, (2) Exploring the user context, (3) Designing the gamification, and (4) Evaluating the gamification. Following a preliminary evaluation, we applied a final design iteration to the app that was implemented in therapeutic practice. However, fewer therapists than expected used the app when given the opportunity and information. In a series of qualitative interviews, we investigated their reasons for not using it. Analysis of the results generated three themes that inhibit eHealth adoption: (1) Fittingness of gamification with individual users, (2) Fittingness of eHealth with face-to-face practice, (3) Distortion of therapeutic alliance by eHealth and gamification. Based on these outcomes and our design process we identified the following three recommendations to enhance implementation and adoption of eHealth in mental healthcare: (1) Align expectations of stakeholders through framing (2) Integrate therapeutic aspects in gamification, and (3) Focus on personalisation.