To create a connection between Adobe Experience Platform (AEP) and Shopify, you'll need to follow the available tutorial. However, if you're encountering an authentication issue, it's important to ensure that you have both the storefront access token and admin access token.
Regarding your question about "{HOST}," this refers to the Shopify domain that you're trying to connect to. This will typically be in the format of your-store-name.myshopify.com. When entering this into AEP, you should replace "{HOST}" with your Shopify domain.
For example, if your Shopify domain is "example-store.myshopify.com," you would enter "example-store.myshopify.com" into the appropriate field in AEP, replacing "{HOST}" with your actual domain name. Make sure to enter the domain name exactly as it appears in Shopify, including any capitalization or special characters.
By correctly entering your Shopify domain in AEP, you should be able to resolve the authentication issue and successfully create the connection between the two platforms.