Product requirements are incomplete because of uncertainty about customer acceptance. What should the project manager do?

When product requirements are uncertain, especially regarding customer acceptance, the most effective agile approach is to gather sufficient requirements to create a Minimum Viable Product (MVP). An MVP allows for early customer feedback and validation, reducing risk and informing subsequent development iterations. This iterative approach is central to agile methodologies. The other options are less effective: Gathering a reduced set of requirements and adding extra features is counterproductive; extra features increase complexity and cost without addressing the core uncertainty. Stopping all project work until all requirements are defined upfront is a traditional, waterfall approach that is ill-suited for situations with high uncertainty and can lead to significant delays. Researching similar products and collecting data on best features is a good practice for market analysis but doesn't directly address the uncertainty of this specific customer's acceptance of this product's requirements.