Understanding Customer Trust in Digital Payment Ecosystems: Evidence from UPI Adoption in India

India’s Unified Payments Interface (UPI) has emerged as one of the world’s largest real-time digital payment systems, processing over 13 billion transactions monthly as of early 2025. Despite this phenomenal macro-level adoption, the behavioural drivers of UPI adoption in Tier 2 and Tier 3 cities remain underexplored. This study empirically investigates the determinants of customer trust and UPI adoption intention through an integrated theoretical framework combining the Technology Acceptance Model (TAM), the Theory of Planned Behaviour (TPB), and Institutional Trust Theory. Drawing on primary data from 215 respondents collected via structured questionnaire between January and February 2026, and analysed using Ordinary Least Squares (OLS) regression, the study finds that Perceived Privacy (β = 0.287), System Quality (β = 0.269), Perceived Security (β = 0.227), and Regulatory Trust (β = 0.193) are significant antecedents of Trust in UPI (R² = 0.469). Trust in UPI (β = 0.535) and Perceived Usefulness (β = 0.288) together explain 45.6% of variance in Adoption Intention. All seven hypotheses are supported at p < 0.001. Findings carry significant implications for fintech firms, banks, and policymakers seeking to deepen digital financial inclusion across semi-urban India.