The current literature gives a strong outline to conceptualise the characteristics of the design of a digital platform. This includes the design strategy, design features and value creation as the primary considerations. These interconnected domains provide a powerful lens to design choices that a contemporary organisation would need to contemplate. However, there is limited attention to conceptualising the mechanisms to explain how a digital platform's layers integrate. Adopting a critical realist philosophy, research was conducted into how HPE Financial Services (HPEFS) designed and deployed a digital platform to grow the business. The in-depth study was conducted as a seven-year longitudinal study and applied the theoretical generative mechanism model from Henfridsson and Bygstad’s (2013) seminal paper. The study contributes to the digital platform literature in a number of ways. The results of the study provide a detailed description of three platform integration mechanisms to explain integration at the architectural level between layers – (1) Capability Appropriation, (2) Layer Complementarity and (3) Value Hybridisation. Digital platform integration mechanisms can explain the inherent properties of design choices that, in turn, influence the digital design and the subsequent value creation outcomes. The study has proven that causal structures exist that can act, in context, on design choices an organisation may make on its digital platform (Pawson & Tilley, 1997). These causal mechanisms, when actualised, will explain the observable outcomes or events to demonstrate their alignment to the seminal work of Henfridsson and Bygstad (2013). From here, they are embedded into a conceptual framework and digital platform design model that outlines the cause-and-effect relationship to explain and theorise what an organisation will experience when designing a digital platform. These are accompanied by a third contribution, the concept of Corrective Mechanisms. They ensure digital platform stability during changes by keeping the underlying deep structure intact and driving incremental improvement without reconfiguration. As a final contribution, abstracted from the generative mechanisms, a set of design principles are formulated to guide a firm's efforts in digital transformation. Building on the digital platform design model, they are established based on (1) Linkages, (2) Complements and (3) Synergies between the layers and components of a digital platform.