Thank you for your response. The link won't work unless you change your hosts file to 188.8.131.52 for this sub-domain name. Details for both Mac and PC at: hidden link
(if you're able to do that) I'd be pleased to send you a log-in account for the WordPress back office by email.
I'm unable to test whether including output='url' will solve the issue at the moment (because my development zone's hosting server is not fully working this afternoon) but as soon as I can respond about that, I will.
I've made some progress by trial and error. The changes I made were recorded in a text file, a screenshot of which is attached.
I'd really appreciate your comments when you have time because I want to code this correctly rather than 'fudge it' myself using trial and error until something happens to work on my computer and on my screen.