I receive an error that says "that number has already been used, use another number to continue" (not those exact words, but message is the same). Is this new?

I understand how frustrating it can be when a feature you depend on suddenly stops working, @gatoraquatics. Allow me to share some information about the error you encountered when creating invoices in QuickBooks Online (QBO).

Before doing so, can you send a screenshot of the specific error message you receive? Knowing the exact error would help me provide the right information you need.

QBO automatically assigns numbers to your transactions unless you turn on custom transaction numbers. This feature has a sequential numbering system where it auto-populates the text number based on the previously entered. You may encounter an error stating that the number already exists if you used the same number more than once or if you've manually input similar digits in the Invoice no. field. See the screenshot below for your reference.

If you want to continue using the same invoice number, you can click Yes. However, if you don't have the option to continue using the same number, you'll want to change it to avoid the error.

In case you need to customize your sales forms to reflect more of your business identity, you can easily modify the details by following the steps in this link: Customize invoices, estimates, and sales receipts in QuickBooks Online.

If you have any other concerns managing your invoices, please don't hesitate to leave a reply below. I'll be here ready to provide additional help to get you back in working order. 

@Nicole_N  RE: You may encounter an error stating that the number already exists if you used the same number more than once or if you've manually input similar digits in the Invoice no. field.... If you want to continue using the same invoice number, you can click Yes.

Or not. Here's what we're getting:

It's a hard stop. No way to continue.

I have questions:

1) Why don't you know this?

2) Why, when the OP states they can't continue do you blithely reply that they can without actually checking to see how QuickBooks works first?

3) Why would intuit do something so stupid as to block customers from recording two or more invoices with the same number?

I need to use duplicate invoice numbers for my customers.  Not only can I no longer input them manually, I turned off the invoice numbers field and am currently getting an error message that I am using duplicate invoice numbers.  I cannot send any invoices to my clients.

It's nice to see you in this thread, @ajohn2. I'll outline some troubleshooting steps below to prevent duplicate invoice numbers in QuickBooks Online (QBO).

First, let's disable the custom transaction numbers on your sales form so the system will apply the default numbering system by sequence. Here's how:

1. Go to the Gear icon and select Account and Settings.
2. Click the Sales tab and select the Sales form content section.
3. Switch off the Custom Transaction Numbers.
4. Click Save, then Done.

If you've already done so, let's perform some troubleshooting options to rule out the possibility of a browser issue. To do that, open your account in an incognito window. You may refer to the keyboard shortcuts below.

• For Google Chrome browser: Ctrl + Shift + N
• For Mozilla Firefox browser: Ctrl + Shift + P
• For Safari browser: Command + Shift + N

Once resolved, return to your original browser to clear its cache or utilize another compatible one. 

We have also received similar reports about being unable to create invoices due to duplicate numbers. I recommend reaching out to our customer support team to add you to the list of affected users. 

Moreover, we have available tools in QBO to personalize your invoices according to your preferences.

Know that we are only a couple of clicks away if you need further help regarding duplicate invoice numbers. The Community team is here to assist you all the time. Have a good one.