Hi @supporteis,
Welcome to the Auth0 Community!
I understand you encountered a scenario where your email template URLs are linked to your custom domain even after downgrading to a free subscription plan.
First, could you please clarify if you have deleted your custom domain in your Auth0 Dashboard > Settings > Custom Domains?
If not, you will have to delete the custom domain to reflect the default Auth0 domain for your tenant.
Once that is complete, you should see your email templates revert the URLs to the default Auth0 domain.
Hoped this helps!
Please do not hesitate to reach out if you have additional questions.
Thank you.