Unfortunately, without knowing your domain name, I am afraid we cannot assist further for troubleshooting.
It could be multiple things:
There is no Universal SSL certificate issued for your domain.
Could be you don’t have an A type of DNS record which is proxied under the DNS tab of Cloudflare dashboard, which prevents the Universal SSL to issue a certificate.
What kind of method for a setup you’ve used, was it Full zone setup or Partial (CNAME).
Was your domain a part of or using SaaS for your Website.
Is there any error under the SSL/TLS tab → Edge Certificates for your domain.
Maybe there’s an issue with the DNSSEC.
Some of the assumptions and we need more feedback from you to those questions for further steps to finding a solution to your case.