403 4xx Client error RFC 3261
SIP 403 Forbidden
The server understood the request but refuses to fulfil it. Authenticating again will not help.
Typical Q.850 / ISDN cause: 21 (Call rejected)
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Common causes
- Wrong credentials after the challenge (some servers send 403 instead of another 401).
- Your IP address is not on the carrier allowlist for IP-authenticated trunks.
- Calling a destination you are not permitted to dial, such as international or premium numbers.
- The account is suspended, or fraud protection blocked the call.
- The caller ID (From or P-Asserted-Identity) is not allowed by the provider.
How to fix it
- Confirm your public IP is registered with the carrier, and check for NAT changes after an ISP failover.
- Check the dial permissions and fraud limits on the account.
- Send caller ID in the format the carrier expects (E.164 or national).
- Check fail2ban or similar tools haven't blocked the IP.
Seeing 403 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 4xx responses
The request has a problem or cannot be completed at this server, usually because of something on the requesting side or the target user.