No. Under the terms, each subscription can carry a single offer or a single discount. If the app is already showing a discount and you enter a code too, the code is calculated on the full original price rather than the discounted one. Vouchers work the same way, coming off the base price.
Certain codes carry conditions stated when they're announced, for example valid only on a first subscription, monthly plans or full-day plans, and certain deals apply only in particular cities or plans. Promo codes expire quickly, whereas gift card, points and compensation codes last one year.
Worth knowing before you sign up: the whole subscription is paid at the start and you can't defer paying for half the period. Prices are in SAR, with VAT and delivery inside the service area already included.
Source: Daily Mealz help center: terms and conditions