The net terms you use for a vendor in Ottimate have to match in your QuickBooks. Having Different net terms in your QuickBooks might prevent the invoice from exporting from Ottimate. 

Here is an example of the flag will appear on top of your invoice if we are unable to export because of this:

To edit your vendor's net terms so you can export click on More and Vendor Mapping.

You can then edit the net terms for your vendor in the pop-up. Make sure it exactly matches your net terms for the vendor in QuickBooks. If your vendor does not have any net terms in QuickBooks you can use "Net 30" as this is the default for QuickBooks.