LEGACY - Why is the invoice number synced to QuickBooks is not the same as it is in Finale Inventory?

This is a limitation to the length of an Invoice number in QuickBooks.

They only allow 11 characters for invoice numbers.
If your order id(number) in Finale is 10 characters or longer it will not be able to be synced into QuickBooks.

Finale Inventory's invoice number will be the Order number plus "-1" for the first invoice and "-2" for a second invoice, and so on. This makes the invoice number longer than the 11 allowed by QuickBooks.  In order to get the record to sync with QuickBooks, we have to convert it into a unique number by using a "hash" number.  You cannot control this number and there is no reference to it in Finale Inventory or QuickBooks that you can see or lookup. 
There is no workaround for this other than to make sure your order numbers are no longer than 9 characters, to begin with.

We will look at future improvements for this scenario with a new integration with QuickBooks Online where we might be able to store the original invoice number/order number in a memo field in QuickBooks.