FP1 – Postcode Shipping Guard

What it does

• Keep your existing Shopify shipping zones — PSG blocks restricted Postcode/Postal/ZIP codes inside those allowed zones.
• When a customer enters a Postcode/Postal/ZIP code at checkout, the app compares it to your rules.
• If a match is found, checkout is blocked for that destination with a clear message.
• Supports both exact matches (full code) and prefix ranges (a group of codes that start the same way).
• Optionally show a short notice in the cart (if you add the theme block) to set expectations before checkout.

How it works

• Your Shopify shipping zones define where you ship in general.
• In Shopify Admin, you add one or more PSG rules (your restricted code list) to create exceptions inside those zones.
• At checkout, the customer’s entered Postcode/Postal/ZIP code is evaluated against your rules.
• If the code is blocked, checkout shows no delivery options for that destination, preventing completion until the customer changes the address.
• If you enable the optional cart notice, the cart can show a short warning before the customer reaches checkout.

How to write rules

• Exact match: block a full code (for example SW1A 1AA or 94105).
• Prefix range: block a group of codes that start the same way (for example SW1A*, 941*, or M4B*).
• Shorter prefix = larger area: SW1A* is narrower than SW1*. SW* blocks a much larger area.
• Spaces are ignored (for example SW1A 1AA matches SW1A1AA, and M4B 1B3 matches M4B1B3).

Country filter (optional — only for multi-country stores)

• Leave this as Not set (recommended) if you sell in one country. Use it only for multi-country shipping, so the same Postcode/Postal/ZIP code doesn’t get blocked in the wrong country.
• If needed, use a two-letter country code (US, CA, GB, AU, etc). If you don’t know it, select “Other” and enter the country code or a common country name.

Key benefits

• Block restricted pockets inside the regions you already allow in Shopify shipping zones.
• Stops orders that you can’t service from reaching fulfillment and creating support tickets.
• Prevents accidental sales to restricted Postcode/Postal/ZIP codes (based on your rules).
• No-code setup — add and adjust rules anytime.
• Optional cart notice helps reduce surprise at checkout.