Purpose: This paper aims to focus on the involvement of mental healthcare professionals in a co-design process of a digital healthcare platform. Many people with severe mental disorders need constant support and monitoring, and with long waiting lists and scarce resources in mental healthcare, there is a dire need for innovative digital solutions to counteract those issues. This paper elaborates on a co-design process of a digital platform and mobile app designed for people with mental disorders. The platform primarily considers two perspectives: (i) the patients and (ii) the healthcare professionals. Design/methodology/approach: This paper is based on canonical action research, where the co-design involvement with 13 healthcare professionals is analyzed and their interactions with three primary scenarios are focused. Findings: The main contribution of this paper is three co-design principles: (i) clarity and information accessibility regarding the patient's side, (ii) efficiency and flexibility when it comes to the healthcare professional's side and (iii) a notification function in the mobile application. Originality/value: The theoretical contribution is the conceptualization of the three co-design principles that others can use when designing digital platforms in healthcare in general and psychiatric care in particular. The practical contributions are firstly outlined through the co-design process itself, where scenarios to guide the work are used, and secondly, the improvements made in the digital platform derived from the results of the co-design process.