I just recreated the same exact setup that worked in a dev tenant in a production tenant with a custom domain. Everything goes smoothly except the actual loading of the SSO dashboard. The logs show it successfully logs into the dashboard but when it gets to this step of the login process:
I have checked your configuration and it seems that your custom domain was correctly configured.
The most likely reason for getting this error in Production and not previously in the Development environment is by reaching the Duplicate Certificate Limit, since we use Let’s Encrypt to issue the SSL certificates for Auth0-Managed Custom Domains, and they are subject to rate limits.
If you delete a Custom Domain and then re-add it a few times in a short period of time, the new certificate may not be issued. I have made the necessary checkings, and I believe this should be the reason of receiving the error message.
This issue can be overwritten by our teams internally by getting the certificate renewed, so I would suggest creating a suport ticket so my colleagues can further assist.