What had worked? I use Windows 2012, but never had such a problem.
Your certificate has only one domain name ( https://check-your-website.server-daten.de/?q=jdcounselling.co.uk ):
CN=www.jdcounselling.co.uk 07.05.2019 05.08.2019 expires in 81 days www.jdcounselling.co.uk - 1 entry
So your non-www version isn’t secure.
|Certificate error: RemoteCertificateNameMismatch|
Create one certificate with both domain names and use that with two bindings.
Or create a second certificate with the non-www domain name and use that (I don’t know if your client has such options).