This study aims to analyze the impact of the transition toward electronic payment systems, specifically instant payments (real-time payments), on the size of the informal economy (the parallel economy). This is conducted through a case study relying on instant transaction data recorded globally and across several pioneering economies in this field, such as India, Brazil, Nigeria, and the European Union. The study proceeds from the hypothesis that the widespread adoption of instant payment channels contributes to narrowing the operational scope of the informal economy by reducing reliance on currency in circulation, broadening financial inclusion, and enhancing the capacity of tax authorities to monitor transactions and expand the tax base. Methodologically, the study adopts a descriptive-analytical approach based on secondary data issued by specialized international institutions, alongside a review of relevant economic literature and the application of a comparative case study method. The study concludes that the relationship between the expansion of instant payments and the decline in the size of the informal economy is generally an inverse one (i.e., the expansion of the former is associated with the contraction of the latter). However, this relationship is neither automatic nor immediate, as it is mediated by institutional, regulatory, and cultural factors. Furthermore, the impact varies significantly between developing and developed economies, contingent upon the degree of financial inclusion and the level of trust in formal institutions. The study recommends that the expansion of instant payment infrastructure must be coupled with a package of incentive-based tax and regulatory policies designed to encourage economic actors to transition voluntarily from the informal to the formal sector............................... Keywords: .................Electronic Payment, Instant Payments, Informal Economy, Parallel Economy, Financial Inclusion, Shadow Economy.