First of all, you should take all the instructions in the control panel. They are often wrong, or at least not the best way to do things. We would change them if we could, but we can’t.
Like KangJL said at the start, you should follow this guide instead:
Looking at your client area, I see you still need to complete Step 2, requesting the SSL certificate. So please start there and follow the rest of the guide.
A private key that doesn’t have a matching SSL certificate. And there is no SSL certificate because the certificate order failed, in part because you created it with the wrong domain name.
Remember: SSL certificates are linked to domain names, not hosting accounts, so you need to request one for the domain you’re actually hosting your website on, not your account’s main domain.
Please request a new SSL certificate for your actual domain name and make sure a certificate is actually issued before trying to install it.