Sales Order credit/debit memos can be created for the following reasons:

• An invoice is posted to the incorrect date.
• An order is sold to the incorrect customer.
• Incorrect items were included in the order.
• Duplicate invoice is created
• A return is not needed but an overpayment or incorrect discount was entered requiring a debit.

1. Open Sales Order, Main, Invoice Data Entry.
2. Click the Next Invoice No (#) button, and select the following:
   • Customer No = The customer to apply the credit memo to.
   • Invoice Type = Credit Memo or Debit Memo
   • Apply to Inv # = The invoice being credited. Important: Do not apply to the invoice if you are trying to correct a posting date. Instead - leave this field blank. It will create a separate Credit memo in A/R. You will then apply this credit memo to the original invoice through cash receipts entry by creating a $0.00 Cash receipt. See article DocLink: How to use Cash Receipts Entry to apply credit memos and prepayments to invoices in Accounts Receivable for Sage 100 ERP
     Note: For Credit Card Processing to automatically create the credit transaction for the original credit card, the selected invoice must have been paid by a saved credit card.
3. Click the Lines tab, and select the items to be credited.
4. Enter all quantities as positive amounts.
   Note: If the entire invoice is being credited, each item must still be selected individually.
5. Print the Memo
6. Print and Update the Daily Sales Reports / Updates (Sales Journal)

In the event you have invoiced the entire sales order inadvertantly, creating a Credit Memo for this invoice will not 're-open' the original sales order. A new sales order will need to be entered

See also Enhancement Request on the Sage Ideas website:

https://www5.v1ideas.com/TheSageGroupplc/Sage100ERP/Idea/Detail/11570: Recall Sales Order when voiding an invoice