can't get certs working with cert-manager
Your ingress is referring to an issuer, but the issuer is a ClusterIssuer. Could that be the reason? I have a similar setup with Issuer instead of a ClusterIssuer and it is working.
I have done this implementation, you can follow this way -
Install jetstack from here
Then follow these steps from this stackoverflow post
Make one clusterIssuer or you can make individual issuer too, once you patch the hostname to ingress, then the tls-certificate in that namespace will be autogenerated by Jetstack after the acme-challenge validation
Kindly make sure to map the IP of loadbalancer nginx/traefik etc to DNS/hostname