> For the complete documentation index, see [llms.txt](https://helpcenter.channable.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://helpcenter.channable.com/css/setup/set-up-the-supplemental-source-for-your-merchant-in-google-merchant-center.md).
# Set up a supplemental source
Set up a Google Merchant Center supplemental source for your Channable CSS product feed.
The supplemental source connects Channable to Google Merchant Center. It's needed to apply CSS optimizations to your existing product feed.
Once set up, optimizations from tools like the [Title Optimizer](/css/optimization-tools/title-optimizer.md) will sync automatically to Google Merchant Center, so Google can use them in your Shopping ads.
{% hint style="info" %}
#### **Migrated from Producthero?**
Create a Channable supplemental source alongside your existing Producthero source. Follow [Add a Channable supplemental source after migrating from Producthero](/css/producthero-migration/migrate-from-producthero-to-channable/add-a-channable-supplemental-source-after-migrating-from-producthero.md).
{% endhint %}
Use this guide to create a Channable supplemental source.
***
### :memo-circle-check: Before you start
**Good to know**
* If you manage multiple feeds in Channable, set up a **separate supplemental source for each feed**.
* Each feed label and language combination has its own supplemental URL. Use the URL that matches your feed, such as `NL/nl`.
***
### :video: Video: How to set up the supplemental source
{% embed url="" %}
{% stepper %}
{% step %}
#### Copy the supplemental source URL in Channable
Option 1: Copy the URL from the overview page
1. Go to **\[your company] > CSS Merchants**.
2. In the **Merchant overview** tab, click :list: to switch to table view.
3. In the **CSS markets** column, click :chevron-down: to expand the Merchant Center account.
4. In the merchant row, click :copy: **Copy URL**. Paste the URL somewhere safe, as you'll need it in step 3.
Option 2: Copy the URL from the merchant dashboard
1. Go to **\[your company] > CSS Merchants**.
2. In the **Merchant overview** tab, click :grid: to switch to grid view.
3. Each card represents a Merchant Center account. Select a merchant to open its dashboard.
4. Click :copy: **Copy supplemental source**. Paste the URL somewhere safe, as you'll need it in step 3.
{% endstep %}
{% step %}
#### Enable Advanced Data Source Management in Google
{% hint style="info" %}
#### Note
Skip this step if this add-on is already enabled.
{% endhint %}
1. Sign in to [Google Merchant Center](http://merchants.google.com).
2. In the side navigation, go to **Settings > Add-ons**.
3. Locate **Advanced Data Source Management**, then click **Add**.
4. In the popup, click **Add** again.
{% hint style="success" %}
**Advanced Data Source Management** should appear in the **Your add-ons** tab.
{% endhint %}
{% endstep %}
{% step %}
#### Add the supplemental source
{% hint style="danger" %}
#### Important
Add the source under **Supplemental Sources** only. Adding it under **Primary Sources** can disrupt your feeds.
{% endhint %}
1. In the side navigation, go to **Settings > Data sources**.
2. In the **Product sources** tab, select **Supplemental sources**.
3. Click **Add supplemental product data**.
1. Select **Add product data from a file**, then paste the supplemental source URL you copied in [step 1](#copy-the-supplemental-source-url-in-channable).
2. At **Edit schedule**, set the update time. We recommend setting this between 10:00 and 12:00 Amsterdam time to keep your feed data up to date. Click **Continue**.
3. At **Feed label**, select the feed label.
4. At **Language**, select the feed language.
5. Click **Select primary data sources**. Google Merchant Center displays sources with the selected feed label and language.
6. Select your primary data source.
7. Click **Create Data Source**.
:circle-info: I see a Fix your product file warning
If Google Merchant Center shows the **Fix your product file** warning, the supplemental source has no data yet.
This warning disappears after you use CSS tools in Channable and data syncs to the supplemental source.
{% hint style="success" %}
#### Supplemental source set up
Your supplemental source is now linked to your primary data source, with Channable able to sync and send information to your Merchant Center account.
{% endhint %}
{% endstep %}
{% endstepper %}
---
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