In the fourth sprint the project manager finds that no customer representatives have participated in any sprint activities and the team reports a prototype is ready. What should the project manager do next?

The best next step is to invite customer representatives to the review meeting. In agile methodologies, continuous customer feedback is crucial for validating work and ensuring the product meets their needs. Since no customer representatives have participated, this meeting provides an essential opportunity to re-engage them and gather critical input on the prototype. Contacting the customer to confirm receipt of updates is passive and doesn't address the lack of engagement or the need for feedback on the prototype itself. Creating a prototype manual is premature; the prototype needs customer validation first to ensure it's the correct solution. Delivering a presentation to the QA team is also premature; while QA is important, the primary concern at this stage is customer validation of the prototype's functionality and alignment with their expectations.