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When using the Create Credit Note operation, by default, the total invoice amount will be prorated against all the line items present in the invoice. Suppose that you edit the credit note amount and create multiple credit notes against a single invoice, then the line items' amounts in such credit notes are arrived at by applying the same ratio as was in the original invoice. This can lead to a small surplus or deficit, which is captured as a fractional correction.
Note: Keep in mind that this amount is not lost anywhere. It will be adjusted in the final credit note that you create for the respective invoice.
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