Adds new promotion code to the cart by its code.
Promotion code is being added as separate cart item line.
export async function addPromotionCode( promotionCode: string, contextInstance: ShopwareApiInstance = defaultInstance, ): Promise<Cart>
|- code of the promotion|
|- instance of the api client (by default it's an Axios instance)|
Example is generated automatically. Sometimes it's required to be adjusted to your needs.