Symptoms

• The application on api-server-02 cannot connect to an external payment gateway at payments.provider.com:443.
• curl https://payments.provider.com hangs and eventually times out.
• DNS resolution works: nslookup payments.provider.com returns the correct IP.
• The same curl command works from other servers in the same subnet.
• The server can reach other external HTTPS endpoints (e.g., https://google.com).
• The issue appeared after a security team member applied "hardening rules" to the server.
• No network-level firewall or security group changes were made.