The SAP B1 Connector tool is configured to update the Sales Order or Purchase Order object, and the DocEntry is mapped to make it find the correct Order. However, when you add new lines it updates the existing lines instead of adding new ones
The default behaviour for the connector tool is to update existing lines using the relevant line number. Therefore default behaviour does not allow for adding new lines.
You need to pass -1 as the linenum so that the tools know that you want to add lines.