Add Finnish postcode validation to Shopify checkout

The problem

Shopify's native shipping zones are coarse — they work by country and region, not by Finnish postcode precision. If you deliver only to specific postal areas, Shopify's defaults either over-permit (accepting orders you can't fulfill) or require complex workarounds.

How Delivery Zone solves it

Call the Delivery Zone API from your Shopify backend (custom app, Shopify Functions, or checkout extension) before the order is confirmed. The API returns a clear deliverability decision and zone-based price you can surface in the checkout UI.

Example API request

# Server-side: check whether a postcode can be delivered to
curl -X POST https://api.deliveryzone.fi/v1/check \
  -H "X-Api-Key: dz_live_..." \
  -H "Content-Type: application/json" \
  -d '{"destinationPostcode":"00100","basketValueCents":4500}'

# response
{
  "canDeliver": true,
  "zone": "Helsinki Center",
  "priceCents": 590,
  "reason": null
}

// Server-side only — never expose your API key in browser code
const res = await fetch('https://api.deliveryzone.fi/v1/check', {
  method: 'POST',
  headers: {
    'X-Api-Key': process.env.DZ_KEY,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({ destinationPostcode: postcode, basketValueCents: basket }),
});
const data = await res.json();
if (!data.canDeliver) {
  showError(data.reason); // e.g. "OUT_OF_ZONE"
} else {
  setShippingFee(data.priceCents);
}

// PHP — server-side, keep API key out of frontend
$r = wp_remote_post('https://api.deliveryzone.fi/v1/check', [
  'headers' => [
    'X-Api-Key'    => get_option('dz_api_key'),
    'Content-Type' => 'application/json',
  ],
  'body' => json_encode([
    'destinationPostcode' => $postcode,
    'basketValueCents'    => $basketCents,
  ]),
]);
$data = json_decode(wp_remote_retrieve_body($r), true);
if (!$data['canDeliver']) return [];
foreach ($rates as $rate) {
  $rate->cost = $data['priceCents'] / 100;
}

Example customer-facing message

We don’t deliver to this postcode. Please check the postcode or choose a different delivery address. Your order has not been charged.

Who this is for

Shopify store owners in Finland

Shopify developers

Shopify agencies building custom checkout flows

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Shopify integration guide Checkout validation use case API reference