The program manager should schedule a call with the vendor PM and vendor executive to review the statement of work (SOW), which is a document that defines the scope, deliverables, timeline, quality, and payment terms of the project. The program manager should clarify the expectations and criteria for user acceptance testing (UAT), which is a process of verifying that the system meets the user's requirements and expectations. The program manager should also discuss the reasons for the UAT failure and the corrective actions needed to resolve the issues. The program manager should not approve the invoice until the UAT is successfully completed, as this would compromise the quality and value of the project. The program manager should also not escalate the issue or work on a compromise without first reviewing the SOW and communicating with the vendor12.