Digital transformation has the potential to profoundly change the way public administrations deliver public services to its users. One of the challenges involved in the inter-organizational networks that often govern integrated digital services is to identify what coordination instruments are effective. In this paper we examine this issue through a case study that deals with the transformation of invoicing services in Belgian public administrations at the federal and Flemish (regional) level. We review the coordination instruments and study how they evolved over time. Our findings suggest that transformation (1) might in part depend on the choice of instruments and multiple mechanisms. The mix of appropriate coordination instruments is likely to change as digital transformation objectives and governance challenges evolve over time. (2) Digital transformation might be a step-by-step process involving multiple rounds of digitalization and its specific implementation contingent on the service itself.