I just paid for an SSL certificate I intended to use on my free DDNS site, but it looks like I need an email associated to the site to actually activate the certificate.
Is it possible to do this with the free DDNS and a home server?

The approval email addresses are a list of pre-approved email addresses by the Certificate Authority and the email addresses such as a Gmail address that is not on the list cannot be used for approval.

An option is to sign up for Email Forward for your domain and receive emails for *@yourdomain at a forwarded email address such as your Gmail address. You may request a refund for the email service when the validation is done.