post https://api.helloextend.com/orders//line-item
This endpoint allows the addition of a single line item to an existing order using the Extend Order ID. Merchants may want to add a line item to an order in the event an order was not completed with a customer or the customer purchased additional products on their existing order. This may also be used in cases where we have to cancel an existing line item because there was an issue or inaccurate data with the original line item and a new line item needs to be created.