Ted here from Shopify, thanks for posting your query!
When I check the domain using What's my DNS here, it appears as though the domains A record and CNAME is not pointing to Shopify correctly. Can you please log into your domain's admin and point the domain to Shopify as mentioned in this guide? Your domain shouldn't have any other A record listed and only 1 www. CNAME attribute listed, as mentioned in the guide. Feel free to share a screenshot of your domain's set up - while blocking out any sensitive information.
As well, any changes you make to the domain can take 48 hours to fully adjust.
Please let me know how this goes! Our live support is also available here if you would prefer a faster response.