Thanks 🙂
Ah, I see the {HOST} you are talking about... this should be populated with your shopify host.. I am guessing that this should be the https://shopify.site.com or https://www.site.com domain...
If this isn't populated correctly, this is likely the main factor in your authentication failing... basically you have provided an account authentication token... but not told it what to actually connect to.
The reason that the screenshot shows {HOST} is that this is sort of a standard placeholder for a value, without posting a real value... honestly though, I would prefer them using something like fakedomain.com or https://www.fakedomain.com so that you can actually see the format that is expected....
When you get the auth tokens from Shopify, does it provide host information? If it does, I would start with that.
Good luck!