In the CSV file, the header is mandatory (first comes the structure and then all the other fields) but the , columns can also be comma or semicolon separated. The first column must be the the structure column followed by any other fields.
When uploading a CSV file the structure field is not mandatory (if you will register "No structures" anyway), but at The structure column can contain a valid chemical file format as listed above for registering Single structure, or can be left empty for registering No-structures. At least one field (e.g. Id or additional data) should must be mapped prior to initiating the upload process . Otherwise, if no field is mapped, or the upload will fail.
Note that in case of CSV files the system might not automatically recognize the fields, so manual mapping should be made in order to successfully upload the file.