When syncing over estimates, invoices and timesheets from LMN to QuickBooks, specific LMN fields will go to specific QuickBooks fields for each type of document synced.
If you are using a specific template in QuickBooks for invoices or estimates you may have more fields than shown in the mapping document. If you've added additional custom fields with a QuickBooks template then LMN data will not map to those.
Anything marked as N/A in the document is a data field that LMN will not sync any information into.
The below document has the mapping for both QuickBooks Desktop and QuickBooks online, one tab for each.