1.Use Postman to manually test the connectivity to the Access Token Endpoint URL from your network environment. This can help identify any connectivity issues or errors returned by the endpoint.
2.Check Endpoint Configuration: Ensure that the Access Token Endpoint URL is correctly configured in your OAuth 2.0 Authentication Profile within Pega. Double-check the spelling, syntax, and any additional parameters required by the endpoint.
@ArnaudW - Issue is with pxIsValidURL validate rule. Verify the DSS regexForAuthProfileURLValidation and need to add below expression. If its present modify if not create a new DSS rule. Its giving issue because of “.” after the server name.