Thanks for posting in the Community, @pattyk. I'd be glad to lend a hand with importing invoices.
First, I'd like to take a quick moment to welcome you to QuickBooks Online Advanced. It's also nice to see that you're taking advantage of the new features in the software.
@Aleh - CloudBusiness is correct in that you will need to have an invoice number when importing a CSV. This is a required column and is largely used to help ensure that transactions are properly grouped. I had a similar experience of needing to include an invoice number for a file that had a single line.
The Custom transaction numbers setting means that the numbers in the Excel file will be pulled over if it's turned on. However, if it's not, then the imported invoices will have their number overwritten by the standard QuickBooks numbers. For example, if your spreadsheet has an invoice marked as 101 then it will not be retained and a default will be used.
Should you not need custom numbers then you can put a default or generic number in there as it will be overwritten. However, please make sure that invoices with multiple items on it share the same number to ensure proper grouping.
Please let me know if you should have any questions about this or anything else as I'm just a few clicks away. Have a good day.
