How do I redirect my old domain to a new domain without receiving an SSL cert error?

I have an old domain name. Lets call it https://www.olddomain.com

I have a new domain that I want to redirect it to.

The issue is that the old domain used to be with a different hosting provider and I have since changed the nameservers back to the provider it was originally with.

The issue I am having is that when I create a redirect in the .htaccess file, I get an SSL cert error.

The http version of the website redirects just fine.

Is there any way to force the old domain name to load in HTTP so that it will redirect correctly? Or do I have to purchase a cert for the old domain in order for it to redirect correctly.

Thank you for your help. I have been Googling this for a while now and can't seem to find a straight a answer.