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.