When the retailer sends an allowance or charge through on an order, the allowance/charge code needs to be mapped properly for a certain item to validate the order lines.

First you need to make sure that an item is specified for the allowance or charge item. Once it is added to the item list of TOE, it needs to be mapped to the allowance code. 

Click on the Cog --> Lists --> Allowances and Charges

Select the code from the list and make sure item is mapped for Header Item Code or Line Item Code accordingly. You need to have separate codes for Header allowance and Line Allowances.