As European cities race to meet climate-neutrality goals, Smart Mobility and Mobility as a Service (MaaS) have emerged as primary technological levers. However, the operational deployment of these systems often reveals profound structural frictions between public administration frameworks and technological realities. Based on the Rouen Living Lab experience within the Horizon Europe SPINE project, this policy brief identifies five systemic hurdles to sustainable MaaS deployment, ranging from procurement-tech lifecycle mismatches to the management of technical debt and the "marketing gap". It outlines pragmatic, replicable strategies for Public Transport Authorities (PTAs) and technology providers, advocating for interoperability as a legal standard and a shift toward industrial, data-driven governance (Tracking-by-Design).