If you need to add a shipping charge or adjust pricing on a customer invoice after the order has shipped or is already in progress, you can do so without disrupting the picking or fulfillment process. Simply make sure you only edit the shipping line item and/or price values on the invoice—no other changes. These edits will not affect fulfillment.
1. Click ‘edit’ on the invoice
2. Go on the invoice and ONLY edit the shipping or price values
3. After you’re done, mark as active