TL;DR
The source file headers must match the configured Source Field values.
The top row must be the headers
All the other rows must be data
Headers must not be duplicated
More details
If column names do not match:
- Data from unmatched columns will not be loaded
- Columns in the spreadsheet or .csv or fields in the .JSON that are not specified in the Source Field list will be ignored during processing
- Important Note: The Source fields in the Inactive tab will be ignored even you have specified the column in the source file.
It is not specified what will happen if you have 2 columns with the same header. It may vary from version to version. It may throw an error, it may take the data from the first, it may take the data from the second.
Having the Source Field slightly different, for example typing "Account ID" in the Source Field mapping but "AccountID" (notice the missing space character) in the spreadsheet header row.
Having a copyright notice above the header row or below the data row, or other information. If you want to do that - put the extra info in a different TAB in the spreadsheet, and then specify the tab that should be processed, other tabs will be ignored. (this is not possible with .JSON)
Having TWO rows for the header is not supported. The second row will be treated as data and likely give you an error when you try to process it. (this is not possible for .JSON)
A very uncommon, but not unheard of, mistake would be to have the header with one (or more) blank line before the data is not allowed.
A mistake that occasionally happens is putting a header for one value and then the contents of that column contains other data. Sometimes it is obvious, but other times it will be subtle, such as 'ID' and 'Name' and you have the Name data in the ID column and ID data in the Name column.
The ORDER of the columns/fields is completely irrelevant.
You can even have blank columns, that will be ignored, This doesn't apply to JSON since you can't have blank fields in JSON.
The WIDTH of the column is completely irrelevant. (.xls & .xlsx only)
The height of the column is completely irrelevant. (.xls & .xlsx only)
The color of the text or background is completely irrelevant. (.xls & .xlsx only)
Use of collapse features is completely irrelevant. Meaning rows in a collapsed section WILL be processed. (.xls & .xlsx only)