Issue Description
Our SIP integration with the OpenAI Realtime API suddenly stopped working. All outbound SIP calls to OpenAI’s endpoint are being rejected with SIP/2.0 403 Forbidden, even though HTTP/WebSocket authentication works perfectly.
What’s Working
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Webhook verification succeeds -
HTTP API calls to accept endpoints work correctly
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WebSocket connections authenticate successfully
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Project settings and billing are confirmed as normal
What’s Failing
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All SIP INVITE requests rejected with 403 Forbidden -
OpenAI leg fails to connect to conference
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Calls reach the user’s phone but no AI audio (silent call)
Current Status
100% failure rate on SIP calls over the past week
Troubleshooting Already Done
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Generated new API key and deployed
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Removed old API key
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Verified FreeSWITCH gateway configuration is correct
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Confirmed project has Realtime API access
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Checked billing status (all normal)
Configuration
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Using FreeSWITCH with TLS transport
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SIP gateway configured with correct endpoint and project ID
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Same setup that was working previously
Question
Has anyone else experienced SIP authentication failures recently? The fact that HTTP/WebSocket auth works but SIP doesn’t suggests this might be a service-side issue rather than our configuration.
Tags (if available):
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realtime-api
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sip
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api-error
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troubleshooting