Using custom domain with namecheap


I have a flask app served at namecheap. The login happens at subdomain level. When I try to use a custom domain with auth0 managed certificate, the verification is not successful.

However, I also have a certificate at namecheap already. When I use self-managed certificate, the verification works but there are additional issues with load balancing etc.

What is the easiest way to solve this issue?
I already have a a subscription at auth0.