I have problem with restore backup.

[Kənan Sahmuradov]

Import failed. Check your server logs for more information. com.atlassian.confluence.importexport.ImportExportException: Unable to complete import because the data does not match the constraints in the Confluence schema. Cause: PSQLException: ERROR: duplicate key value violates unique constraint "unq_lwr_username" Detail: Key (lower_username)=() already exists.

[Brant Schroeder]

@Kənan Sahmuradov 

This should help you work through this issue. https://confluence.atlassian.com/confkb/confluence-site-xml-import-fails-with-duplicate-key-error-438993638.html

[Kənan Sahmuradov]

I saw it.but solution didnt work

[Brant Schroeder]

Does the instance that you are importing from still exist?  If you could validate that no duplicates exist in the database and then perform the backup again.