From time to time, promo codes are utilized when certain advertising initiative are implemented.
If you have received a promo code, you can utilize it only on the web app (see app.invintorywines.com).
1) Visit https://invintorywines.com/ and click "Get Started" in the top right
2) After creating an account, when you get the Prestige pop-up, sign up and then enter your code during checkout
Once you've subscribed to Prestige on the web, you can download the app on your phone and access Prestige there as well (you just can't input promo codes on the phone due to Apple restrictions, which is why I always tell people to sign up on the web. If you've already created an account on your iPhone, then just log in on the website and click on Prestige along the left menu to access the paywall and enter your code).