Creating a new invoice but it says the invoice number has already been used. I went into sales and searched but dont see that invoice number used.

I'm here to ensure you successfully create an invoice, taskservices. 

If an invoice with the same number already exists, QuickBooks Online (QBO) may display an error notice. To eliminate repetition, simply enter a different number. However, since you mentioned that the invoice number has never been used and you attempted to type another number, you should first disable your custom transaction number.

Turning this option off allows the system to use its default numbering system for transactions. When you disable the custom transaction numbering function, QuickBooks automatically assigns sequential numbers to transactions. This ensures that each transaction is assigned a unique number in sequential order. This automatic numbering system will eliminate manual entry, so you won't have to worry about assigning numbers yourself. It will also decrease the possibility of duplicate numbers, which is a common problem when assigning numbers manually.

Here's how to turn it off: 

1. Go to the Gear icon located at the upper right corner and choose Account and Settings. 
2. Click the Sales menu.
3. Within the Sales form content section, press the Pencil icon for you to make some changes. 
4. Toggle off the Custom transaction numbers. 
5. Click Save. 
6. Once you're done making changes, press Done. 

If the issue persists, it's best to use other supported web browsers or private browsers to rule out any browsing history or cached files causing the problem. Here are the shortcut keys for accessing private browsers:

• Google Chrome: press Ctrl + Shift + N
• Mozilla Firefox: press Ctrl + Shift + P
• Microsoft Edge: press Ctrl + Shift + N
• Safari: press Command + Shift + N

To personalize and add some specific info to your invoice and other sales forms, you can refer to this material: Customize invoices, estimates, and sales receipts in QuickBooks Online.

You're always welcome to ask us again if there's anything else you'd like to know more about. Just leave it in the comment section, and we'll be right there to assist you in no time.