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Validation Function

The validation function ensures MUP compliance at checkout by blocking orders that violate minimum unit pricing requirements.

Setup Required

Important: The validation function must be added to your checkout rules manually:

  1. Go to Shopify Admin → Settings → Checkout
  2. Scroll to Checkout rules section
  3. Click "Add a checkout rule"
  4. Select "Cart validation" as the rule type
  5. Find and select "MUP Validation" function
  6. Click "Save"

The function is automatically deployed with the app, but must be added to checkout rules to be active.

What It Does

Before a customer can complete checkout, the validation function: 1. Checks if customer is in Scotland 2. Validates product prices after discounts 3. Blocks checkout if price per unit < MUP floor 4. Shows error message to customer

When It Runs

The validation function runs: - When customer attempts to checkout - Before payment processing - After discounts are applied

What It Checks

Price Validation

For each product in cart: 1. Gets final price (after discounts) 2. Calculates price per unit 3. Compares to MUP floor 4. Blocks if below minimum

Address Detection

The function also checks: - Billing address postcode - Shipping address postcode - Detects Scottish postcodes automatically

If a Scottish postcode is detected but region is not set to Scotland, shows warning.

Error Messages

Price Violation

Message: "Minimum Unit Pricing (MUP) applies to this order. The discounted price of [Product] is below the legal minimum of £0.65 per alcohol unit. Please remove your discount code or return to cart to review pricing."

Action required: - Customer must remove discount code - Or return to cart to review

Address Mismatch

Message: "Scottish address detected ([Postcode]). Please return to your cart and select 'Scotland' as your region to ensure correct pricing and MUP compliance before completing your order."

Action required: - Customer must return to cart - Select Scotland as region - Return to checkout

Order Tagging

Orders with address mismatches are tagged: - MUP_NON_COMPLIANCE - Address mismatch detected

These tags help identify orders needing manual review.

Troubleshooting

Validation not blocking checkout? - Verify validation function is added to checkout rules - Check that function is enabled in checkout rules - Ensure MUP enforcement is enabled - Review function logs for errors

Validation blocking incorrectly? - Check product total_units metafield - Verify minimum unit price setting - Review discount code configuration

Not blocking when it should? - Ensure MUP enforcement is enabled - Check customer region is Scotland - Verify validation function is active in checkout rules

For more help, see Troubleshooting.