Can user-migration work on federated share?

User-migration-app sounds great, a question to help one of my user take out from my instance :
Is it supposed to work on a federated shared export-file ?
This appears to be not working here.
What have been done :

  • create export in the app
  • federate shared it to his new nextcloud
  • importing report succes but no files appears

Any clues ?