This study investigates the effect of interoperability on digital payment adoption among 400 Commercial Bank of Ethiopia (CBE) customers in Bahir Dar City, with PU as a mediating variable, using an explanatory, cross-sectional, correlational, quantitative design guided by the Technology Acceptance Model (TAM). Structural equation modeling (SEM) via AMOS 23 revealed that institutional interoperability had the strongest direct effect on adoption (β = 0.217, p < 0.001), followed by operational (β = 0.188, p < 0.001) and technical interoperability (β = 0.152, p < 0.001), while financial interoperability was not a significant predictor (β = 0.029, p = 0.171). Perceived usefulness was significantly predicted by institutional (β = 0.479, p < 0.001), technical (β = 0.388, p < 0.001), and operational interoperability (β = 0.306, p < 0.001), but not by financial interoperability (β = -0.047, p = 0.147), and PU itself significantly predicted adoption (β = 0.229, p < 0.001), confirming its mediating role. These findings indicate that interoperability influences digital payment adoption both directly and indirectly through perceived usefulness, with institutional and technical interoperability emerging as the strongest drivers; the non-significance of financial interoperability likely reflects Ethiopia's early adoption stage. This study extends TAM to the Ethiopian context and provides empirical validation for the National Digital Payment Strategy.