In the index page for the site that is on the sub-domain on the other site I have put a navigation link to the other site.
If I click on this link it reports page not found. this is because the code adds the sub-domain proceeding the link I have set in the index.html on the sub-domain. This is the link it shows in the browser:
https://coppermine.1066cards4u.co.uk/ww … lying.club
In the html code for the page where the navigation link is on the sub-domain is shown below: