📞 Common SIP Response Codes

Code	Meaning	Use Case
100	Trying	Provisional response to an INVITE
180	Ringing	Call is alerting the destination
200	OK	Successful request
403	Forbidden	Request rejected, e.g., bad credentials
486	Busy Here	Callee is busy
487	Request Terminated	Call canceled or timed out
500	Internal Server Error	Temporary failure
503	Service Unavailable	Server is down or overloaded