If you see an error message stating File contains unknown headers when uploading the CSV file to the bulk manage subscription tool:

1. Note the listed properties within each [ bracket ].
2. Open your CSV file and remove the columns that match up with the properties listed in the error message.
3. Review your CSV file and formatting to ensure the included columns and rows are maintained.
4. Upload the CSV file again in the Import your subscriptions menu.
5. Click Next, and you should now see Preview your mapping instead of the error message.