Error: "CANNOT VOID INVOICE. You can void only invoices that have not had any adjustment activity."

You can't void a vendor invoice that has had any transaction activity posted against the invoice.  To void you will use a credit memo.  If the invoice is a negative dollar amount, use a debit memo.

1. AP, Invoices, Credit Memos
2. Select the Vendor Id
3. For Apply to, select "Invoices"
4. For Invoice #, select the invoice number
5. Enter the Date for the Credit Memo (Generally the same date as the invoice date)
6. Enter the Amount of the invoice.
7. For Account #, select the same GL account number debited when the invoice was created.
8. Post

Option 2: To void a negative Vendor invoice by performing a debit memo:

1. AP, Invoices, Debit Memos
2. Select the Vendor Id
3. For Apply to, select "Invoices"
4. For Invoice #, select the invoice number
5. Enter the Date for the Debit Memo (Generally the same date as the invoice date)
6. Enter the Amount of the invoice.
7. For Account #, select the same GL account number creditedwhen the negative invoice was created.
8. Post

How to void Accounts Payable (AP) vendor invoices or invoice credits