1. Check that the website or web application is reachable from the other network endpoint.
2. Make sure the able to access URL or IP address is whitelisted in the firewall.
3. Check if the DNS records are configured correctly and the corresponding entries are propagated correctly.
4. Verify that Windows firewall is not blocking the connection to the website or web application.
5. Review if the machine on which AD user is logged-in is part of the corresponding domain.
6. Check if the user’s account is added to ACL in AD if applicable.