For the Let's Encrypt option to work the site must point to the server you are installing the SSL on. This is because Let's Encrypt will place a file in a folder (.well-known) which they will call to verify the certificate.
If you have any redirects on the site that might stop this file from being called, the SSL issue with fail as well.
Login to your panel at https://controlpanel.hostinguk.net
Login through https://billing.hostinguk.net/
Go to Services
> My Services
> Click on the Active button for your MS Dev package
Click Login to Control Panel
Once Logged in
Go to 'Websites
' and click on your website
Go to the SSL Tab and click Install Certificate
under the Let's Encrypt
You should get a green message to say if this has completed:
Then try browsing to your site at https://
For any further issues, please contact support.