Uploading a spreadsheet into either a Group or your Contact List does require specific formatting.
First, please confirm that the spreadsheet is saved as either a .xls or .csv file.
Next, confirm that your spreadsheet follows the below header requirements:
You can also click here to watch a quick Video on Spreadsheet Uploads!
If you are still having problems please contact support (firstname.lastname@example.org) so we can assist you further.