The header line must contain a tab-delimited list of column identifiers. The column identifiers must match the API attribute names defined for the given API. These correspond to the "Column ID" of the spreadsheet columns.
For example:
ProjIdTABProjNameTABProposedDateTABEstimatedCost
The header values are the API attribute names (spreadsheet Column ID values), not the column captions used for spreadsheet import. This is a key difference between API data and spreadsheet
import formats.