Stakeholders reject a feature at sprint review. What next?

First I stay curious rather than defensive. The Sprint Review is meant to inspect the increment and gather feedback, so rejection is information, not failure.

1. Understand why. Ask what exactly is wrong: missing need, wrong behavior, usability, or a changed priority. Capture the feedback verbatim.
2. Separate the causes. Did we misunderstand the requirement, did the need change, or was the quality poor? Each leads to a different fix: better refinement, a backlog change, or a stronger Definition of Done.
3. Decide with data. Adjust the Product Backlog: rework, reshape, or drop the item, and re-order it against other work. Dropping is a valid outcome, because we avoided more investment in the wrong thing.
4. Close the loop. Agree with stakeholders what "good" looks like and when they will see the next version.
5. Inspect the process in the retrospective, for example by involving stakeholders earlier, with prototypes or mid-sprint demos.

The Product Owner remains accountable for the resulting backlog order.