<p>Omnichannel retailing enables retailers to address challenges from digital transformation and the COVID-19 pandemic. Understanding what motivates customers to stick with an omnichannel retailer and make repeat purchases is critical. While existing research has primarily focused on retailer-centric perspectives and seamless customer experiences, customer-centric factors—such as omnichannel synergy, defined as the added value created by integrating multiple channels and resources—remain underexplored. This study addresses this gap by integrating the dedication-constraint (DC) model with key contextual factors, including omnichannel synergy and transaction costs, to examine customer post-adoption decisions, specifically omnichannel stickiness and repurchase intention. The DC model elucidates how dedication mechanisms (desire for long-term relationships, reflected in omnichannel synergy and customer-brand engagement [CBE]) and constraint mechanisms (past investments and benefits, reflected in seamless experience [SE], transaction costs, and calculative attachment) influence customer behavior. Based on a quantitative survey of 802 omnichannel users, supplemented by in-depth interviews and focus group discussions, the findings reveal that (1) dedication and constraint mechanisms explain 74% of the variance in customer stickiness and 69% in repurchase intention, (2) omnichannel synergy accounts for 61% of CBE variance, and (3) SE and transaction cost-savings explain 41% of calculative attachment. This study shifts the focus of omnichannel research from traditional retailer-centered metrics to customer-centered perspectives, offering a cross-disciplinary model that underscores the pivotal role of omnichannel synergy in shaping post-adoption behaviors. Retailers are advised to invest in the four pillars of omnichannel synergy—horizontal, vertical, strategic, and financial—to strengthen customer retention and drive repeat purchases through integrated channels, strategic partnerships, and cost efficiencies.</p>