Error 99001 means a required field is empty on a row. The template marks some fields as required for the product type, and a row that reaches Amazon with one of those fields blank returns error 99001.
The processing report gives five entries for each failed row: the record number, the SKU, the error code, the type, and a message. Record 1 is row 3 of your file, so the row for a record sits at the record number plus two. For error 99001, the message names the field that is missing its value. The report names the field and leaves the value to you. The correct value is a fact about your product, and the report carries nothing about your product beyond the file you sent.
The set of required fields depends on the product type, and the Data Definitions sheet of the template states which fields are required for yours. The column stands in the file and the cell is blank. Amazon reads an empty required cell as a missing part of the product record, and the row is returned until the cell carries a value.
Each upload goes through Amazon's processing again before the result comes back, so a row cleared in full in one pass saves the processing wait of a second pass.
A submission can carry errors that sit outside the file. A missing brand registration or approval returns error 5665. A missing permission to list in the category returns error 8026. Editing the file does not repair either one. The diagnosis lists those errors separately, with the reason and the step to take in Seller Central. If every error in your diagnosis belongs to that group, we charge nothing.
The free diagnosis reads your failed file and the processing report Amazon returned. It shows every error by SKU, states which errors we fix automatically, which ones need your answer, and which ones the file cannot fix. You see the full breakdown before you pay anything. You can start from the FixFlatFile home page.
Requirements differ by category, and Amazon decides whether a file is accepted.