Do discounts, invite links, and gift codes work on App Store subscriptions?

No. Discounts, invite links, Patron gift links, and gift cards work for website signups only. They can't be applied to a subscription started in the App Store, and gift cards can't be redeemed in the iOS app.

To use one, start your first membership on the web at glass.photo and use the link or code when you sign up. Codes are for a first subscription, so they can't be added to a membership that already exists.

If you're subscribed through the App Store and want to move to the web, see Can I switch between Apple ID and Email login?.