Conventions

Casing

Event names: snake_case. Use add_to_cart, not addToCart or AddToCart.
Parameter names: snake_case. Use item_id, transaction_id, currency.
These are the GA4 standard names — the agency maps them to Meta names (AddToCart, Purchase…) in GTM.

Data types

Expected type	OK	Not OK
Number (prices, values)	`price: 42.00`	`price: "42.00"`
Number (quantity)	`quantity: 2`	`quantity: "2"`
String (IDs, names)	`item_id: "BIO-001"`	`item_id: 1`
String ISO 4217	`currency: "EUR"`	`currency: "€"`

⚠️ No thousands separator: 1299.50, never "1,299.50" or "1 299,50".

⚠️ Units, not cents: 42.00 (€), not 4200.

When to push

Event type	When to push
`view_item`, `view_item_list`, `view_cart`	After the page/section renders
`add_to_cart`, `remove_from_cart`	After the server confirms the cart mutation (not on optimistic click)
`begin_checkout`	When the user lands on step 1 of checkout
`add_shipping_info`, `add_payment_info`	After step validation (submit OK)
`purchase`	Once, on the confirmation page, after DB commit
`refund`	When the refund is issued (back-office)
`search`	After results render
`sign_up`, `generate_lead`	After server-side confirmation

Product ID — the golden rule

The item_id you push must be identical to the id in the Meta Catalog feed and Google Merchant Center.

Source	Field
Site (dataLayer)	`items[].item_id`
Meta Product Catalog	`id`
Google Merchant Center	`id`

Recommended: use the main SKU (e.g. BIO-CRM-001). Not internal DB UUIDs.

For variants (size, scent): item_id: "BIO-CRM-001-50ML" + item_variant: "50ml".

`purchase` idempotency

purchase must be pushed exactly once per order. Refreshes on the confirmation page must not re-push.

Options:

Redirect immediately to a confirmation page that doesn't re-push on refresh.
Persist the pushed transaction_id in localStorage and skip if already there:

const txId = 'ORD-2026-00123';
const pushed = JSON.parse(localStorage.getItem('bio_pushed_tx') || '[]');
if (!pushed.includes(txId)) {
  window.dataLayer.push({ ecommerce: null });
  window.dataLayer.push({ event: 'purchase', ecommerce: { transaction_id: txId, /* ... */ } });
  pushed.push(txId);
  localStorage.setItem('bio_pushed_tx', JSON.stringify(pushed.slice(-50)));
}

Debugging during dev

In the browser console:

window.dataLayer
// → array of every event pushed since page load

window.dataLayer.filter(e => e.event === 'purchase')
// → just purchases

More debug tools: Debug tools.

GTM snippet

The agency will provide the exact snippet. Plan to insert:

<!-- In <head>, before any other script -->
<script>
(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
'https://load.analytics.biosphereskincare.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
})(window,document,'script','dataLayer','GTM-XXXXXX');
</script>

<!-- Right after <body> -->
<noscript><iframe src="https://load.analytics.biosphereskincare.com/ns.html?id=GTM-XXXXXX"
height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>

⚠️ The snippet uses load.analytics.biosphereskincare.com (first-party) instead of www.googletagmanager.com. Intentional — bypasses ad blockers.

Casing​

Data types​

When to push​

Product ID — the golden rule​

purchase idempotency​

Debugging during dev​

GTM snippet​