Sometimes when editing one of your ads you may find that your ad is already using URL parameters. You this is easily identified if you spot a "?" symbol anywhere in your Website URL. The most common URL parameter on Shopify would be the variant, which you will see if your product has multiple versions, i.e. different sizes or colors

If your product page uses a variant, then you will need to adjust your UTM parameters so that you do not use more than one "?" symbol. Instead of pasting your UTM code with "?" symbol, you will paste the code in with a "&" symbol instead.

For example, if your Website URL on your Facebook ad is:

www.test.com?variant=123456

Then instead of adding:

?comet_source={{site_source_name}}&comet_ad_id={{ad.id}}&comet_placement={{placement}}

You would need to add:

&comet_source={{site_source_name}}&comet_ad_id={{ad.id}}&comet_placement={{placement}}

So your final Website URL would be:

www.test.com?variant=123456&comet_source={{site_source_name}}&comet_ad_id={{ad.id}}&comet_placement={{placement}}

Once you have the UTM code setup correctly for the variant code, you can go ahead and publish your ad.