How to validate if a discount code exists before checkout? 🎫

### Explanation It is not possible to validate discount codes before checkout in Shopify's frontend. This is a security feature to prevent enumeration of valid discount codes. Available options for handling discount codes: 1. Customers can enter discount codes during checkout 2. Discount codes can be applied via URL parameters 3. Store owners can create automatic discounts that don't require codes The `cart.discount_applications` Liquid variable only shows already-applied discounts (including both automatic and code-based discounts), and the price_rules endpoint is part of the Admin API which should not be exposed to the frontend. Reference: [Shopify Discounts Documentation](https://shopify.dev/docs/themes/pricing-payments/discounts)