Hi MikeCA3,

Let me show you how to change the sorting of invoice number on your reports. 

1. Go to Reports tab and select a report or you may choose Invoice List report. 
2. Click on Sort drop-down menu. 
3. On Sort by drop-down menu select No.
4. On Sort in, select whether you would like the invoice number show in Ascending order or Descending order.

Please note that the steps provided above only applies when you generate a report from the Reports tab. 

For your reference, you can check on this article on how to set up custom invoice numbers [Video]. 

Feel free to post your questions here in the Community if you need more help with QuickBooks Online.