1. Create the extra custom field you need via “Inventory Products Settings”. For detailed steps, see the guide on how to create custom product fields.
2. From the “Templates” dropdown, go to “Printable Templates”.
3. Click “Invoice/Estimate Layout”.
4. Choose the template you want to add the field to.
5. Select “Item Columns”.
6. In the “Field” section, choose the custom field you created earlier.
7. Click “Save”.
8. When you create an invoice, select the template you modified, the custom field will appear as a column in the item lines. For more details, refer to the How to Create a Sales Invoice guide.