If I have multiple users (program leads) creating invoices in QBO Advanced, can I trust QBO to keep the invoice numbering straight - and just auto-generate?

Yes, you can generally trust QBO to keep the invoice numbering straight and sequential, even with multiple users creating invoices concurrently, Romina.

To activate automatic and reliable numbering, ensure that the Custom transaction numbers feature is turned on. This allows you to assign a starting invoice number which will serve as the reference point for generating sequential number for future invoices.

Here's how:

1. Navigate to the Gear icon and Account and settings. 
2. Go to the Sales tab, and select the pencil icon .
3. Make sure to turn on the Custom transaction numbers option for automatic number for invoicing. 
   
4. Click Save and Done.

Once enabled, you can begin creating an invoice and set a starting number to ensure that subsequent invoice numbers are automatically generated in sequential order. After completing the setup, remember to disable the Customer transaction numbers feature to prevent any unintended modifications to invoice numbers moving forward.

However, if a user attempts to modify the settings and unintentionally creates a duplicate invoice number, the system will also automatically alert them that the invoice number is already in use. I've added a screenshot below:

If you have any questions and concerns about creating invoices, feel free to reach out. We're always here to assist you.