Hi there, David. One of your invoices was likely created when the duplicate invoice warning was dismissed, either accidentally or during simultaneous activity by another user. That’s why you see two invoices with the same number.
Yes, you can void the unpaid duplicate to keep your accounts accurate. Before doing so, make sure it’s truly a duplicate and not a separate transaction that should exist with a different number. Compare the line items, dates, and amounts to confirm they are identical. Once the duplicate is voided, your customer balances and accounting records will remain correct.
To prevent this from happening in the future, go to Settings > Account and Settings →>Sales. Make sure that 'Custom transaction numbers' is turned off, then click Save and Done. This will allow QuickBooks Online to automatically generate unique, sequential invoice numbers for you.
If you have any additional questions, feel free to comment on this thread.
