Quickbooks Online has their own invoice numbering system. However, there is a field in Quickbooks that will show the 17hats invoice number.
Please note, the below image invoice number in 17hats is 150.
Once the invoice is synced to Quickbooks Online, you can view the invoice within Quickbooks by clicking on the "View Invoice in QuickBooks" link. Please note that the field titled "Message displayed on invoice" has the 17hats invoice number.
KeyWord Search: invoice, QuickBooks, Bookkeeping, Number