Sorting Line Items
The Opportunity Products List on the Opportunity can be in any order:
By default, we will sort the opportunity products based on Sort Order, Created Date, and Name.
Created Date
The basic order will always be the created date of the opportunity products.
When we add/create multiple opportunity products at the same time, we can add them based on various filters, e.g., Name, Product Code, List Price, or any other field in the list view.

Hence, the created date becomes invalid for sorting/ordering purposes.
Sort Order
The standard Sort Products functionality provided by Salesforce helps rearrange the opportunity products in the list.
Opportunity products will have a blank value in the Sort Order field unless we have used the sort functionality at least once.

Suppose the default ordering provided by Breadwinner does not work in the various scenarios in which opportunity products are sorted in Salesforce. In that case, you can retrieve the child records in a specific order and send them to NetSuite in that exact order. This can be referenced using another field on the child object: