Interoperability remains a major challenge in citizen-centred digital government, particularly when services that should be experienced as a single life event are delivered through disconnected institutional procedures. This paper examines that challenge through the case of newborn registration in Mozambique and frames it as a model-based information systems development problem. Using a design science research approach, we employ DEMO to diagnose the existing coordination structure and then develop a lightweight ArchiMate-oriented artefact to support service redesign. The main result is a DEMO-to-ArchiMate modelling pipeline that links diagnosed coordination failures to an architectural representation of interoperability in a life-event service. From the case, four design requirements are derived and operationalised through five constructs: inter-agency life-event service, interoperability agreement, authoritative semantic asset, orchestration capability, and reusable integration pattern. As an exploratory design-science study, the paper evaluates representational adequacy for redesign, not implementation effectiveness or organisational adoption.