Monthly exports are tempting to paste together. That works only when their columns mean the same thing and appear in the same order. A city value under an amount header is a valid looking cell with the wrong meaning.
CSV Dataset Merger appends two CSV datasets after checking their ordered headers. It does not perform a database join.
Match the header before the records
Give both files the header name,amount. If the first contains Ali,1200 and the second Sara,1800, the merged output contains both rows beneath one header.
A second file headed amount,name is rejected even if it contains the same two column names. Reorder that file first. The check avoids moving values into the wrong positions by assumption.
Duplicate removal compares complete rows in the merged data. Two rows with the same name and different amounts are both kept. There is no latest record selection or matching by invoice number.
Know which kind of combination you need
Appending adds more records with the same shape. Joining adds fields by matching a key. This tool handles the first task only. To attach customer addresses to an order list, use a proper join in a spreadsheet, database or data workflow.
Choose the correct delimiter for both inputs and keep quotation marks around cells containing that delimiter. Quoted multiline notes are part of their records and should not be edited into separate lines.
The merged dataset is bounded to 500 records, and the input size limit can be reached earlier. A larger archive needs a file based process rather than repeated browser pasting.
Before sharing the result, inspect one row from each source and review the duplicate count. That checks both the column alignment and whether the repeated rows you removed were genuinely redundant.