add_discount.graphql

mutation addDiscount {
	orderEditAddLineItemDiscount(
		id: "gid://shopify/CalculatedOrder/5678"
		lineItemId: "gid://shopify/CalculatedLineItem/121314"
		discount: { percentValue: 20, description: "Upsell" }
	) {
		calculatedOrder {
			id
			addedLineItems(first: 5) {
				edges {
					node {
						id
						quantity
					}
				}
			}
		}
		userErrors {
			message
		}
	}
}