During project execution, the finance team discovers they were not involved in building the business case and will not approve the estimated ROI. What should the project manager do?

The correct answer is to arrange a meeting with the product owner and finance team to agree on corrective actions. This is the most proactive and effective approach. The finance team's refusal to approve the ROI is a significant issue that directly impacts project viability and requires immediate attention and collaboration. Involving the product owner (or relevant stakeholder responsible for the business case) ensures that all key parties are present to discuss the discrepancy, understand the finance team's concerns, and collaboratively develop a solution. Reviewing the communications management plan might be a subsequent step if communication breakdowns are identified, but it doesn't resolve the immediate financial approval problem. Reviewing the scope management plan and recording it as a risk is insufficient; this is an active issue, not just a potential one. Continuing development and resolving the issue after delivery is highly risky and could lead to project cancellation or significant rework later, making it an unacceptable option.