Enforcement Rules of Value-added and Non-value-added Business Tax Act Article 23

The incentive bonus earned or paid by a business entity in accordance with a sales contract shall be treated as purchase or sales discount, respectively.
中文原文 加值型及非加值型營業稅法施行細則第23條
營業人依經銷契約取得或支付之獎勵金,應按進貨或銷貨折讓處理。

English translation for reference only; the Chinese text prevails. Not legal advice.