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# How to choose a Product Identifier?

# What you will learn
In this article, you will learn:
* [What is a Product Identifier?](#3-what-is-a-product-identifier)
* [When to use Product ID, Variant ID, Metafield, or Custom ID (template)](#3-when-to-use-product-id-variant-id-or-metafield)
* [How to set up your Product Identifier](#3-how-to-set-up-your-product-identifier)
* [Frequently Asked Questions](#3-frequently-asked-questions)

### What is a Product Identifier?

Every tracking event that contains product data — such as View Content, Add to Cart, Initiate Checkout, and Purchase — includes an identifier for each product. This is the value your marketing channels use to recognize **which product** the event is about. For example, it is sent as `content_ids` on Facebook, TikTok, Pinterest, and Snapchat, or as `item_id` on Google Analytics 4 and Google Ads.
Marketing channels match this identifier against the items in your **product catalog or feed**. This matching is what powers:
* **Catalog/dynamic ads**: showing visitors the exact products they viewed or added to cart
* **Product audiences**: building retargeting audiences based on product interactions
* **Product-level reporting**: attributing revenue and performance to the right catalog items
If the identifier in your events doesn't match the ID in your catalog, the channel cannot connect them — your dynamic ads may show the wrong products or stop delivering, and product reports become inaccurate. That's why choosing the correct Product Identifier is important.
By default, TagFly uses the **Shopify Product ID**, which works for most stores whose catalogs are synced directly from Shopify. If your catalog uses a different identifier — such as GTIN, MPN, barcode, or an internal SKU — you can change this setting so your events always match your catalog.

### When to use Product ID, Variant ID, or Metafield

###### Product ID
**When to use:** When your product catalog on the marketing channel uses Shopify Product IDs.
* This is the default option and recommended for most stores
* No additional setup is required
**Example use case:** A store whose catalog is synced directly from Shopify (e.g., via the official Facebook & Instagram or Google & YouTube sales channel), so catalog IDs are Shopify Product IDs.

###### Variant ID
**When to use:** When your catalog is built at the variant level and each variant is a separate catalog item.
* Events will carry the Shopify Variant ID of the purchased/viewed variant
* Useful for stores where size, color, or other options are advertised as individual products
**Example use case:** A fashion store running catalog ads where each size/color variant is a separate catalog item.

###### Metafield
**When to use:** When your catalog or feed uses a custom identifier that is stored in a product metafield — for example GTIN, MPN, barcode, or an internal SKU. This is common when your catalog is uploaded by a third-party feed app or managed manually.
* TagFly reads the value of the selected metafield for each product and sends it as the product identifier, in place of the Shopify Product ID
**Example use case:** A store whose catalog feed is generated by a feed app using GTIN, while Shopify Product IDs are not present in the catalog at all.

###### Custom ID (template)
**When to use:** When your catalog IDs are composed of multiple parts, so no single Shopify field matches — most commonly when your Google Merchant Center feed uses composite offer IDs such as `shopify_VN_1234567890_9876543210`.
* This option is currently available **only for Google Analytics destinations**
* You build the identifier from a template that combines your own static text (prefixes, separators) with tokens:
    * `{productId}` — the product's numeric ID, falling back to the variant ID when it is missing
    * `{variantId}` — the variant's numeric ID
    * `{sku}` — the variant's SKU, falling back to the variant ID when it is empty
    * `{targetCountry}` — the country of the market the shopper is browsing
**Example use case:** A store whose Merchant Center feed is generated by the Google & YouTube sales channel, where offer IDs follow the format `shopify_{country}_{product ID}_{variant ID}`. The template `shopify_{targetCountry}_{productId}_{variantId}` reproduces this format, so GA4 events match the feed exactly.

### How to set up your Product Identifier

* When you create or edit a destination, move to the Product Identifier section:
![](https://storage.crisp.chat/users/helpdesk/website/-/8/3/8/3/8383e5404a31c000/image_361533.png)
* Select the option that matches your catalog: **Product ID** (default), **Variant ID**, or **Metafield**, **Custom ID (template)**

If you select **Metafield**, there are two ways to choose it:
**1. Choose from list**
* Select one of your store's product metafields from the dropdown
* Metafields are displayed as `name (namespace.key)` — for example: `category_2 (test_data.binding_mount)`
**2. Enter manually**
* Click **Enter manually** and type the metafield in the format `namespace.key` — for example: `custom.gtin`
* Use this option if your metafield doesn't appear in the list
||| The metafield value must match the product ID in your channel's catalog **exactly**. If the values don't match, the channel cannot match events to your products, which may affect your catalog/dynamic ads performance.

If you select **Custom ID (template)**
* Enter a **Template** that combines the available tokens with your own separators or prefixes — for example: `shopify_{targetCountry}_{productId}_{variantId}`
* Your template must include at least one of `{productId}`, `{variantId}`, or `{sku}`. Without one, every product would get the same ID, and Merchant Center rejects identifiers that are not unique
* If your template uses `{targetCountry}`, select a **Default country**. It is used when the shopper's market cannot be determined. The value is pre-filled from your shop's registered address — which is not always your primary market — so check it against the market your feed is built for
* Review the **Preview**, which shows a sample product rendered with your template. Compare it against a real offer ID in your Merchant Center feed — a misplaced separator is something validation cannot catch

### Frequently Asked Questions
1. **Does changing the Product Identifier affect my existing setup?**
No. Existing destinations keep using Product ID until you change this setting yourself. The setting applies per destination, so you can use different identifiers for different channels.
2. **My metafield doesn't appear in the list. What should I do?**
Use **Enter manually** and type it in the `namespace.key` format. Make sure to include the namespace — for example `custom.gtin`, not just `gtin`.
3. **Why don't I see the Custom ID (template) option?**
Custom ID (template) is currently available **only for Google Analytics, Google Ads, Facebook, Tiktok and Pinterest**. For other channels, choose between Product ID, Variant ID, and Metafield.

### Need help?
If you run into any issues or want help configuring, reach out to the TagFly support team via the in-app chat — we're happy to walk through it with you.