A project manager is leading a hybrid project funded by a time and materials (T&M) agreement. The project was completed, and the client accepted the delivery of the product. One week later, the client asked the project manager to fix two defects they found in the product. The project manager responded with an estimate of time and money and asked the client to confirm this. The client disagreed and insisted that the work should be done for free because it is a defect in the product.

What should the project manager have done to prevent this?