Currently in the reporting API, the promo code details are shared only when the discount type is set to MARKETPLACE_PROMOTION. 

In some cases, when the promo code is not applied directly, and the Atlassian licensing team applies it Manually, the discount type is set to MANUAL and for that discount type, the promo code details are not shown. 

We have a request to show the promo code details fields even when the discount type is MANUAL so that the partners are aware of the codes used on each transaction and can use the reporting data more efficiently.