The institutional environment significantly shapes entrepreneurial outcomes in developing economies, yet granular, longitudinal analyses of its impact on firm growth trajectories in West Africa remain scarce. This study investigates the specific institutional challenges constraining enterprise development and analyses their differential impact on the growth pathways of small and medium-sized enterprises. A sequential explanatory mixed-methods design was employed. First, a quantitative analysis of longitudinal firm-level data was conducted. This was followed by in-depth qualitative interviews with founders and stakeholders to explicate the mechanisms behind the statistical relationships. Quantitative analysis revealed that firms perceiving high regulatory instability were 40% less likely to achieve sustained growth. Qualitative data identified a pervasive theme of 'navigational capital', where successful entrepreneurs develop informal networks to circumvent formal institutional voids. Formal institutional weaknesses fundamentally redirect entrepreneurial effort towards informal coping strategies, creating a dual ecosystem that advantages well-connected firms while stifling broader-based formal sector growth. Policymakers should prioritise regulatory predictability and simplify compliance procedures. Support programmes must move beyond generic training to actively help entrepreneurs build legitimising connections within both formal and informal networks. institutional voids, entrepreneurial growth, mixed methods, regulatory environment, navigational capital, West Africa This paper provides a novel, integrated analysis of longitudinal quantitative data and rich qualitative evidence to delineate the mechanisms by which institutional challenges are navigated, offering a nuanced framework for understanding entrepreneurial ecosystems in similar contexts.