Digital Product Passports (DPPs) are increasingly discussed as key enablers for advancing the Circular Economy (CE), as they enhance data transparency and support circular strategies across the 9R framework, including Reuse, Repair, Remanufacturing, Repurposing, and Recycling. However, despite their conceptual potential, the specific mechanisms through which DPPs enable these strategies and the barriers limiting their adoption remain insufficiently understood. The study addresses this gap by conducting a Systematic Literature Review (SLR) that synthesizes existing research and structures the identified challenges into six dimensions: Technological, Organizational, Economic, Legal, Societal, and Environmental. These barriers are conceptually mapped to CE strategies, revealing where limitations most critically constrain circular value creation. The findings show that unresolved issues in data quality and interoperability, limited organizational capabilities, misaligned economic incentives, regulatory uncertainty, low user acceptance, and trade-offs between ecological benefits and the environmental costs of digital infrastructures significantly hinder DPP deployment. Building on these insights, the paper develops a structured research agenda that outlines key directions for addressing these challenges and advancing DPP-enabled circular practices. Overall, the study provides a comprehensive synthesis of current knowledge, uncovers significant blind spots in the literature, and lays a foundation for future research and practical implementation of DPPs to accelerate the transition towards a circular economy.