Customers are expected to play a fundamental role in the transition to a decarbonised and digitalised energy system. However, experience so far suggests that customer engagement in energy markets cannot be given for granted. This report investigates those barriers hindering customer engagement in flexibility markets and discusses strategies for their mitigation, aiming to unlock the untapped potential of the resources located at the customer’s premises and foster a more consumer-centric power system. Drawing from an extensive and multi-disciplinary literature review and benefiting from interactions with OneNet cluster demonstrators, this research identifies economic, behavioural, legal, and technical barriers to customer engagement in flexibility markets. Tailored recommendations are provided to surmount each of these barriers, advocating, among other things, for value stacking support, targeted awareness campaigns, regulatory adaptations, and robust infrastructure enhancements.