How to generate a running number within exports?

In case you want to generate a running number, select the field "Consecutive Numbering":

This number is not affected if there are multiple items/rows in the order.

Generate a running number within orders

If you also want to generate a number within the orders, select the field "Position":

For instance: If a customer purchases three products within a single order, the "Position" field will assign a sequential number to each order line.