Hello

1. In Shopify settings in UNA you've used wrong URL. You've used full URL of Shopify account admin panel  instead of a domain only, like my_store.myshopify.com 

2. In your Shopify account products didn't have 'Search engine listing preview' section. I've contacted with Shopify support and they found out that Online Store wasn't enabled on your account. I've added it via 'Sales Channels' -> 'Add'.

3. Then I created a 'Test Product' and everything is working fine now. You are welcome to check it.

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Best Regards
Anton