According to the Agile Practice Guide, the product owner is the person who is responsible for defining and prioritizing the product backlog, and ensuring that the product meets the customer's needs and expectations (Section 3.2.2). The product owner is also the key stakeholder who has the authority to accept or reject the work results, and to make the final decisions regarding the scope and requirements of the product (Section
3.2.3). Therefore, if there is a requirement that conflicts with the product owner's requirements, the product owner is the one who should analyze the new requirement and make the final decision, in collaboration with the other stakeholders and the project team. This is also consistent with the PMBOK Guide, which states that "the project manager should work with the product owner to ensure that the project delivers the agreed- upon features and functionality" (Section 5.1.2.2). References:
* Agile Practice Guide, Section 3.2.2, Section 3.2.3
* PMBOK Guide, 6th Edition, Section 5.1.2.2