Can I restore a deleted invoice number?

It's possible, Cory.

I'll give you some tips for handling your invoices.

You can enable the Custom transaction numbers feature if you want to use the delete invoice number from the Account and Settings. I'll show you how.

1. Go to the Gear icon, and select Account and settings.
2. Click the Sales menu.
3. Turn the radio button on for the Custom transaction numbers under the Sales form content section.
4. Hit Save, then Done.

Following that, you can generate a new invoice and manually enter the invoice number you want to restore in the Invoice no. area.

For future reference, you can visit this link for guidance if you want to personalize the appearance of your sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Let me know if you have additional questions about this procedure. I'll be here to support you.

You can't restore that whole invoice with the invoice number, but you can create a different invoice with same information and set a custom invoice number for that invoice but you have to first enable the custom transaction number setting from your accounts and settings ➝ sales section.