IDX20803: Unable to obtain configuration

hi team,

below is the code to get the document:
IConfigurationManager configurationManager
var discoveryDocument = configurationManager.GetConfigurationAsync(ct).Result;

I am seeing below exception suddenly, the code was working fine:

{“IDX20803: Unable to obtain configuration from: ‘https://.auth0.com/.well-known/openid-configuration’.”}

what could be the reason, can someone assist me on this?