Directly speaking it could get frustrating if you have a coupon and you can not use it. There's the AliExpress Coupon which can be used to purchase anything from any store. To make it easier you could see here something which could get your attention https://www.dontpayfull.com/ To activate a coupon, you'll see the option on the checkout page before making a payment. You can use the app or the website. if you don't see any usable coupon, then know you don't have a matching coupon to use for that particular product you are interested in.
Sometimes the best Aliexpress coupons are handed out to people who don't really need them, new users. All year round, in order to get a profitable coupon you will just need to register on the site.
Some regular customers even go for tricks. They drop their old profiles and create new ones, while receiving a coupon upon registration. And the face value of such a coupon can be both 100 and 200 dollars.