Hi David,
Thank you very much for sharing these options with me. I don't have Google Analytics for the subdomains so I tried the second option.
I selected 'domain name provider', went with 'other', and added a txt record to the DNS configuration for the main domain as per Google's instructions yesterday. I just checked the status a minute ago and I'm still seeing the verification failure message coming up as below:
"Your verification DNS TXT record was not found. You might need to wait a few minutes before Google sees your changes to the TXT records."
How long does it normally take to verify a property this way?
Thanks again David for your kind help.