Adding line items from a Requisition and importing line items into a RFQ Sourcing event

Created a sourcing event using the line items from the requisition (Req) with a complex SPO outcome.  However, when trying to import additional line items to the RFQ received following error message (Column 4 is invalid. This may be because the column name is invalid; the column is at the wrong position or the file is not of proper type. Please refer to the instructions file for more information.that one of the columns is not correct.)  This particular file (line items) has been successfully uploaded to a RFQ without using the Requsition.  The file was saved as Text (Tab delimited) (*txt)  Does the file name/format have to be different when using the line items from the Req and importing line items?  If not, any suggestions on how I can get this to work.  Also, can you make the line item a set amount established by the buyer that the supplier cannot change but will be added to the quote total after RFQ closing?