Hi @ComputerHabit
Column header in csv file is not a necessary option. There are six columns needed in your CSV file -- the first three are your source values, each providing detail about where your data is currently located. The remaining three columns indicate the site, document library and optional sub-folder to where you are migrating your data. All six columns must be accounted for in the file, even if you are not needing a value for a given field.
Column A: Enter a file share path. Required.
Column B: Leave this column blank. This column does not apply to file share migration.
Column C: Leave this column blank. This column does not apply to file share migration.
Column D: Enter the SharePoint site URL or OneDrive email/URL where the files are to be migrated. Required.
Column E: Enter the name of the document library in the SharePoint site where the files are to be migrated. Required.
Column F: Enter the name of the subfolder in the document library. If this column is left empty then the files will be moved to the root level. Optional.
For more information about using a comma-separated value (CSV) file for bulk upload, you could refer to:
https://learn.microsoft.com/en-us/sharepointmigration/mm-bulk-upload-format-csv-json#using-a-comma-separated-value-csv-file-for-bulk-upload
https://learn.microsoft.com/da-dk/sharepointmigration/how-to-format-your-csv-file-for-data-content-migration#use-a-csv-file-for-bulk-upload
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