My client wanted his website republished under a new domain that was shorter. So we pointed the new domain to the website server and "forwarded" by 301 redirect from the old domain hosted on GoDaddy to the new domain (HTTPS).
Now, all of the old links on Google bring up the warning that it is not secure even though the final domain is secure. An SSL certificate is done for the website (new domain) and not the old domain with no website attached as it is only being used for the redirect.
Please advise! Do I duplicate the site under the old domain, add SSL, and then redirect each page to the new domain to avoid any duplication issues with SEO?
*I am very new to this and not too technically savvy.