In Scrum, when Developers encounter difficulties in delivering an Increment due to a lack of understanding of a functional requirement, they should collaborate with the Product Owner. This collaboration is crucial as the Product Owner has the responsibility to clarify the items in the Product Backlog and to ensure that the Development Team understands the work to be done. The Product Owner is accountable for maximizing the value of the product and must work with the Development Team to find out what is feasible and acceptable for the Increment being developed. This approach aligns with the Scrum principle of collaboration and self- organization within the Scrum Team.
The Scrum Guide and the Professional Scrum Product Owner™ (PSPO I) materials emphasize the importance of collaboration between the Product Owner and the Development Team to ensure a clear understanding of the Product Backlog items and to optimize the value of the work being done