403
SIP
403 Forbidden
The server understood the request but is refusing to fulfill it. Authorization will not help. The request should not be repeated.
When You See This Code
When the server policy denies the request regardless of credentials. Common for blocked numbers, restricted routes, or ACL violations.
How to Fix
Check server ACLs and routing policies. Verify the caller is permitted to make this type of call. Contact the server administrator if the block is unexpected.
Specification
Related Codes
Cross-Protocol Equivalents
Compare With
Guides
401 Unauthorized vs 403 Forbidden: When to Use Each
Security & Authentication
SIP Response Codes: Understanding VoIP Call Flow
Real-Time Protocols
SIP Call Flow: Understanding Session Setup
Real-Time Protocols
WebRTC Signaling with SIP and WebSocket
Real-Time Protocols
RFC 3261: SIP Protocol Deep Dive
Protocol Deep Dives
TLS 1.3: Faster, Simpler, More Secure
Protocol Deep Dives
Debugging Scenarios
Specifications
Glossary
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Request Method (HTTP Verb)
TLS Handshake
Authentication
TCP/IP
Port Number
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SIP INVITE
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Codec Negotiation
SIP Response Classes
VoIP (Voice over IP)
Presence (SIP)
PBX (Private Branch Exchange)
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TLS Versions