Users can add invoices from 2 screens:
1) Shipment Level-
Go to the Shipment tab and select Air/Sea/Land.
Click on the edit icon for your shipment.
Click on the accounting section in the shipment.
There you can add customer invoices using the Add Customer Invoice(AR) button.
2) Accounting Tab-
Go to the accounting tab and click Receivable.
A drop-down will appear.
In the drop-down click on the invoice button.
Click on the edit button for the required shipment and update your invoice.
