Adding a certificate to my www subdomain

I have a standard GoDaddy SSL Certificate for my domain (mydomain.com) and I have a subdomain (http://www.mydomain.com/)

When I bought the certificate through Azure it said the certificate would cover the root domain (mydomain.com) plus its www subdomain.

I have bought the standard certificate. I have my certificate working for my root domain just fine. But when I try to add my certificate to my subdomain (http://www.mydomain.com/) it does not add properly.

I click on my 'not secure http://www.mydomain.com' 'add binding'. I import the app service certificate. It validates and then it 'successfully adds the app service certificate to the app'. But then I am still left with http://www.mydomain.com/ not secure and the option to add binding still. 

There is an example on microsoft of it being done as follows 

but when I try have the host name mydomain.com,http://www.mydomain.com it does not allow the comma or spaces.

The certificate does cover the www subdomain, there just seems to be no way to add it.