This thesis explores which UX-challenges third-party app teams might face when developing apps for a digital platform, along with what UX-strategies could be used to overcome these UX-challenges. The study is based on a case study where the software company "Kist” participated. Semi-structured interviews were performed to investigate third-party app development within Kist, focusing on apps used on the digital platform Confluence cloud. The concepts of behavioural and emotional usability were also used to analyse what part of the app’s UX each challenge and strategy focused on. The study shows that the most reoccurring UX-challenges in app development for Confluence cloud relate to behavioural usability, rather than emotional usability. Those behavioural challenges were: creating an app that is easy to use, performs well inside the digital platform, and effectively solves users’ problems. The app should not have too many complex functions, and user actions must follow specific security guidelines. The app’s flow for specific user actions should also not differ too much from the digital platform. These factors can add additional learning curves for users, which will affect the app’s performance and ease of use. UX-strategies with a behavioural usability focus have also turned out to be more applicable than strategies focusing on emotional usability. Confluence cloud and the apps inside serve as business tools. Hence, it is more important that the app performs well inside the platform, is easy to use and effectively helps users solve daily work issues, rather than generating feelings such as joy or attachment.