Over 800 million people globally lack official proof of identity, with sub-Saharan Africa bearing a disproportionate share of that deficit. This article analyses the emerging architecture of Digital Public Infrastructure (DPI), with specific focus on foundational digital identity systems, open-source deployment models, and cross-border payment interoperability. Drawing on Ethiopia's Fayda programme, the Modular Open Source Identity Platform (MOSIP), Africa's pan-continental payment initiatives, and Latin America's Pix-driven experience, the analysis identifies structural constraints, governance risks, and private-sector investment opportunities. The central argument is that Africa's ability to realise the AfCFTA's projected $275 billion trade dividend depends materially on sovereign, open-source digital rails deployed at continental scale.