The quickbooks online invoice number and Fusebill Invoice number are not the same.

If Fusebill is unable to create the invoice in Quickbooks online the first time, it will reattempt to create the invoice and not include the invoice number in any follow up attempts. This allows quickbooks online to generate its own invoice number. 

 To make a correction for this, the number can be changed in quickbooks online: https://quickbooks.intuit.com/learn-support/en-uk/manage-customers-and-income/how-to-change-an-invoice-number-video/01/239358#M20