In case an owner or operator declines to use the National appeal procedure but still wishes to complain about a detention decision, such a complaint should be sent to the flag State or the recognized organization (if authorized to act for the flag State), the Paris MoU informed.
The flag State or Recognized Organization may then ask the port State to reconsider its decision to detain the ship.
If the flag State or the Recognized Organization disagrees with the outcome of the investigation as...
https://safety4sea.com/paris-mou-deadline-for-submission-of-2019-detention-review-cases/