I think the issue is the fact I used two different emails for creating my Shopify and Namecheap accounts. I think the issue would be resolved if I changed the ownership of the domain in my Namecheap dashboard to the email I used for my Shopify. Howev...

I get an error "Your domain is already claimed by a different account. Click below to transfer the domain claim." (with the "transfer my domain" button below) when trying to connect the Google merchant account via Google and youtube app on Shopify. C...