If you've created a Performance Max campaign, but it has yet to start running, this may be caused by an unclaimed website URL.
You can identify this issue by seeing a red banner in your Merchant account:
To advertise your business using Google Merchant Center, your domain must be:
Verified - verify that you have ownership over your website.
This can be done by adding an HTML tag or uploading an HTML link to your website.
To verify your website, click Verify & Claim website on the red banner.
Claimed - Associating your domain with the Google Merchant Center.
This step can be completed by the user who verified the website after it has been verified.
After verifying your website URL, click Claim website in your Merchant's Business Information dashboard.