You get this error in Shopify when you have registered an incorrect URL address on your Smart Send user. You need to make sure that the URL address on your Smart Send user matches your Store URL on your webshop.
- Login to your Smart Send user and edit your website URL to the correct .myshopify.com
- Go to websites and chose the website settings
- In the tab Website Profile change your URL so it matches your Store URL.
You can always find your Shopify Store URL in the Smart Send app on your webshop in the tab connect.
- When you have updated your URL you can go back to your shop and set th app to production mode.