MyWorks Sync supports syncing orders containing discounts/coupon codes into Xero, utilizing the Discount column within the Xero invoice or quote.

Syncing Discounts to the Xero "Discount" column

By default, MyWorks Sync will sync any discounts in a WooCommerce order to the Xero column field for Discounts.

These can be present in the WooCommerce order as either a “discount” field within one or more line items - or as a coupon in the order itself. 

This would be shown in the Xero order in the following example.