I assumed, wrongly as it turned out, that I simply needed the IP address of the server on which our web site is stored but that didn’t work.
Your assumption was correct. However, it might be that your webserver’s *outgoing* IP address is different to the *incoming* one. Or, it might be that the webserver blocks outgoing connections. You will need to ask your web hosting company.
For the outgoing IP address, you can also go to the ‘Advanced Tools’ in UpdraftPlus, find the HTTP tool, enter https://ipinfo.io as the address to visit, and then press the “Fetch (Curl)” link. This should then report back your outgoing IP address.
David