If you opened your completed spreadsheet and Excel gave you an SYLK error, don't sweat. It's a little, albeit annoying, Excel quirk.
If the first cell is named "ID", Excel will get confused and not be able to open your file. If you rename it "id" or "Id", it will work.
This is a rare error, but you might encounter it if, for example, you downloaded a CSV from your CRM, uploaded it to Geocodio, then tried to open it in Excel.