When you see the yellow warning “Cart data needs attention” in your Google Ads conversion tracking diagnostics, it means your Purchase conversion event isn’t passing valid or complete product-level sales data — specifically, the items array required for Google Ads to understand which products were purchased.
Let’s go step-by-step to fix this in Google Tag Manager (GTM), using a GA4 ecommerce dataLayer as your source.
⚠️ What the “Cart Data Needs Attention” Warning Means
This diagnostic message typically appears in Goals→ Conversions → Diagnostics → Cart data when:
- The Google Ads Purchase tag is missing the items array.
- The array exists but lacks one or more of these required keys:
- id (product/item ID)
- price
- quantity
- id (product/item ID)
- Your Merchant Center feed IDs don’t match the item_id values.
- Or the data format is invalid (not an array of valid objects).
Step 1: Enable Product-Level Sales Data in the Purchase Tag
In Google Tag Manager → Google Ads Conversion Tracking (Purchase):
- Scroll down and check “Provide product-level sales data”.
- Set the Data Source to Custom Fields.
- You’ll see a field called Items — this is where we’ll insert the correct array.
If this field is left empty or malformed, your conversion will record — but Google Ads won’t know which items were sold, triggering the “Cart data needs attention” warning.
Step 2: Understand What the GA4 Items Array Looks Like
If you already use GA4 ecommerce tracking, your website likely pushes an items array into the dataLayer during a purchase event.
Here’s an example of what a GA4 items array looks like:
“items”: [
{
“item_id”: “SKU_12345”,
“item_name”: “Cotton T-Shirt”,
“price”: 19.99,
“quantity”: 2
},
{
“item_id”: “SKU_67890”,
“item_name”: “Denim Jeans”,
“price”: 49.99,
“quantity”: 1
}
]
This structure is perfect for GA4 but not automatically compatible with Google Ads — which expects a simplified version of this array.
Step 3: Convert the GA4 Items Array to the Google Ads Cart Items Format
Now we’ll create a Custom JavaScript Variable in GTM to map the GA4 format into what Google Ads expects.
Code:
function() {
var items = {{dlv – items array}}; // GA4 items array from your dataLayer
return items.map(function(item) {
return {
id: item.item_id.toString(),
price: parseFloat(item.price),
quantity: item.quantity ? parseFloat(item.quantity) : 1
};
});
}
🔍 What this code does:
- Takes your GA4 items array.
- Maps each product to a simplified object for Google Ads.
- Ensures:
- id → string
- price → number
- quantity → number (defaults to 1 if missing)
- id → string
Step 4: The Final Output (Cart Items Array)
After running the above transformation, your final Cart Items array — which Google Ads receives — will look like this:
[
{
“id”: “SKU_12345”,
“price”: 19.99,
“quantity”: 2
},
{
“id”: “SKU_67890”,
“price”: 49.99,
“quantity”: 1
}
]
This is the correct structure Google Ads expects in the Items field when “Provide product-level sales data” is enabled.
Step 5: Assign the Variable in Your GTM Tag
- Go back to your Google Ads Purchase Conversion tag in GTM.
- In the Items field, select the new Custom JavaScript variable you created above.
- Save and publish your container.
- Test in Preview Mode:
- Complete a purchase.
- Check that the items array appears correctly in the conversion payload/debug view.
- Ensure each item has id, price, and quantity.
- Complete a purchase.
Step 6: Verify in Google Ads Diagnostics
After a few conversions (usually 24–48 hours), check your Google Ads diagnostics:
Goals→ Conversions → Purchase → Diagnostics → Cart Data
If everything is correctly implemented, the warning “Cart data needs attention” will disappear — replaced with a green check and the message “Cart data is excellent.”