I am trying to figure out how to add a tracked item for a new customer but I don't exactly understand the documentation. What is in the context of your API specification?

items[][itemCode] No (see notes) Your code for this tracked item. Limited to 36 characters.
items[][quantity] No (see notes) The positive amount accurate to up to 4 decimal places that you wish to set the current usage to for this item. Can be zero.

For example, can i do the following or should i do it some other way?

            $newCustomer['items'][1]['itemCode'] = 'MY_ITEM';   
            $newCustomer['items'][1]['quantity'] = 1;