Your "home directory" is /home/username
When you setup a domain, the files for the domain go in the directory called /home/username/domain
When you first log into FTP, you are in /home/username though your FTP client will show it to be the directory root, /.
So you should see in your FTP client these directories:
And just access domain, and you are now at /home/username/domain, and this is where index.html should go.
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