It should be possible to have your CDN redirect http to https, and then have your ingress forward to cert-manager.
But without knowing more, it's not going to be possible to help you.
At a very minimum, please share the error messages you got from Let's Encrypt trying to issue the certificate.
Sharing the domain name would also be helpful for anyone diagnosing. So would sharing your cert-manager configuration.
Additionally, you may get more help in the cert-manager communities like their Slack.