SSL on sub-server not working

I have a domain ‘dafc.co.uk’ and a subdomain ‘shop.dafc.co.uk

Virtual Sub-Server
In domain shop.dafc.co.uk

Parent virtual server dafc.co.uk

I have created a certificate :
Web server hostname shop.dafc.co.uk Issuer name COMODO RSA Domain Validation Secure Server CA
Issuer organization COMODO CA Limited Expiry date May 27 23:59:59 2018 GMT
Certificate type Signed by CA

somehow I don’t think https is working for the site. any ideas what else I need to setup ?
https://shop.dafc.co.uk doesn’t show any secure icon.

thanks for any pointers

brian