Innovation in a digital world increasingly revolves around open platforms that consist of a core technology and a large variety of complementary products developed by an ecosystem of independent complementors. The platform ecosystem literature has mainly focused on indirect network effects arising from the quantity of complements, with little attention to the quality of complements, despite the importance of quality for the complementary value that drives platform ecosystems. Because digital products are malleable and dependent on the ever-evolving ecosystem, we advance a relational and dynamic conceptualization of complement quality. Drawing on a systematic, in-depth qualitative case study of the Philips Hue connected lighting platform and its complementary third-party apps, we study how and why complement quality is sustained over time. By analyzing apps and their updates, we developed a process model that explains pathways through which complement quality is enhanced, maintained, or deteriorates. Changes in the platform core, changes in other ecosystem elements, and idiosyncratic connections by users result in expanding affordances, materializing glitches, and emerging obsolescence. Without further action, glitches and obsolescence lead to deteriorating quality. Joint action of complementors, platform owners, and users is needed to act upon affordances, glitches, and obsolescence, in order to maintain integrity and enhance functionality. This paper contributes to the literature on innovation in platform ecosystems by explaining the dynamic and relational nature of complement quality in a digital platform ecosystem and showing the interdependence of ecosystem members (the triad between platform owner, complementors, and users) in sustained development efforts.