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First thing I notice is the subdomain - blog.novad.com.au is not actually pointed to your Droplet with DigitalOcean. You’ll need to create an A record for blog.novad.com.au and set it to point to 159.89.85.117.
Once you do, you can continue with the tutorial you posted and create an Apache config file so that your Droplet knows what should load when your domain is called.
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