A duplicate invoice, corrected

• Accounts receivable notices ITEM001 was invoiced twice by mistake, once correctly and once as a duplicate. No goods were ever shipped for the duplicate. You raise a credit memo for the duplicate quantity and set Inventory Handling to Credit Only - No Stock Change.
• On posting, in addition to the normal +5 unit entry for your original line, the extension automatically inserts and posts a second, internal entry for the same item: -5 units, at $0.00, tagged internally so it's never shown to users on the document itself.
• Result: the two entries net out (+5 and -5 = 0), so on-hand inventory for ITEM001 is unchanged before and after posting. The customer/G-L side is still credited the full $100.00. This is straightforward arithmetic (a quantity and its exact negative always sum to zero) and doesn't depend on any Business Central classification rules, so it's the option you can rely on with the most confidence.