Your template must be in a .csv file format when being uploaded to the portal.
A .csv file means ‘Comma Separated Values’. It’s the only type of file that our Partner Portal Transaction Reporting app can read. When you save your template, make sure you click “Save As…” and click “Save as type:”, choose the option that says “CSV (Comma Delimited)”.
If you are having trouble interpreting the Column header names in your template, a straightforward way to make the column headers be readable is to click the top-left corner above the “1” row and “A” column, to highlight all rows and columns. Next, put your cursor between two columns, such as column “A” and “B” where there is a line separator, and double click. This will expand each column and enable you to see the entire name of the column header.