This study investigates how ecosystem actors collaborate in the early stages of ecosystem emergence to create and test the ecosystem value proposition. It analyses multi-actor data from a two-year-long experimentation process around the circularization of human waste in France. In doing so, the findings of this study open a black box of collaborative experimentation and uncover important struggles based on the different framings of value and power that become pertinent during the experimentation process. This study contributes to ecosystem literature, by shedding light on the importance of internal legitimacy between ecosystem actors in ecosystem emergence, and to the strategic experimentation literature by showing how multiple theories of value in collaborative experiments lead to negative, yet generative experimentation outcomes.