According to the PMBOK® Guide, the scenario describes a situation where deliverables reached the customer but failed to meet the specified requirements. This indicates a breakdown in the Manage Quality and Control Quality processes. To avoid this, the project manager should have conducted Quality Audits.

The Role of Quality Audits: A quality audit is a structured, independent process used to determine if project activities comply with organizational and project policies, processes, and procedures. It is a key tool in the Manage Quality process.

Prevention of Non-conformance: Audits help identify inefficient or ineffective policies being used on the project. By conducting these audits early and often, the project manager can ensure that the " process " of building the features is correct, which results in a product that actually meets the requirements.

Closing the Gap: Audits confirm the implementation of approved change requests and ensure that the team is following the Quality Management Plan. If the team was deviating from requirements, a quality audit would have flagged this internal inconsistency before the product ever reached the customer for testing.

Why other options are incorrect:

Option A: Engage customer earlier: While stakeholder engagement is important, the prompt specifies that the features did not meet requirements. This is a technical quality issue, not necessarily a communication issue. If the requirements were already documented, the team failed to build to those standards.

Option C: Validate Scope: This is the process of formalizing acceptance of the completed project deliverables by the customer. Validate Scope is where the customer found the problem. You cannot " Validate Scope " to avoid the problem; validation is the point where the failure is officially recognized.

Option D: Validate quality requirements: This is not a standard PMI process name. While you " Plan Quality Management " to define requirements, " validating " them usually refers to the internal verification of the deliverables themselves (Control Quality), which is governed by the processes checked during a Quality Audit.