i used dynamic variable system__call_sid to be sent over as parameter on a webhook tool on the conv | ElevenLabs | Page 1

next mauveBOT Mar 23, 2026, 4:38 PM

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AI-generated Answer for mattyg1997

Short answer:
system__call_sid is only populated during actual Twilio phone calls. In any non‑Twilio context (e.g., web/widget tests, agent simulator) or when you use the dashboard’s test “placeholders,” the platform substitutes the tool parameter with the placeholder value you configured—hence CALL_SID_PLACEHOLDER. Use a real Twilio call path to get a real SID, or avoid referencing this variable outside Twilio calls.

Why it happens

Twilio‑only variable: system__call_sid is defined as “Call SID (twilio calls only).” If the conversation isn’t a Twilio phone call, there is no real SID to inject. (elevenlabs.io)
Placeholders in testing: The Dynamic Variables UI supports setting “placeholders” for testing. When you test from the dashboard (or otherwise don’t supply a runtime value), the placeholder is inserted into tool params. (elevenlabs.io)
Pre‑call webhook fields: On real Twilio inbound calls, ElevenAgents includes call_sid in the webhook payload (so a true SID exists then). (elevenlabs.io)

How to fix

Trigger the tool during a real Twilio call so system__call_sid is available. Use the native Twilio integration or your Twilio flow that connects to the agent; the platform will pass call_sid on inbound and the system variable will be set. (elevenlabs.io)
Don’t rely on system__call_sid outside Twilio. For channel‑agnostic correlation, use system__conversation_id instead. (elevenlabs.io)
If you must test without Twilio, set a realistic test value in the Dynamic Variables “Set placeholders” UI, understanding it will be used in place of a real SID during tests. (elevenlabs.io)
If you’re using SIP trunking (not Twilio), the platform exposes call metadata via caller_id/call_id as system dynamic variables rather than a Twilio SID—use those for that path. (elevenlabs.io)

References:

Dynamic variables (system__

light violet Mar 23, 2026, 4:46 PM

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but they called on a twilio number tho ? and the twilio data show a call sid . but why on tool it has that place holder thing

next mauveBOT Mar 23, 2026, 4:46 PM

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AI-generated Answer for mattyg1997

Short answer: system__call_sid only exists on Twilio phone calls. If your tool shows CALL_SID_PLACEHOLDER, you’re seeing the test/default placeholder you configured for that parameter, not a resolved system variable.

Why this happens (per docs):

system__call_sid is a system dynamic variable that’s available “for Twilio calls only.” On non‑Twilio conversations (e.g., web widget, simulated tests), it won’t populate. If a placeholder is set for a tool parameter, that placeholder value is what you’ll see during testing. (elevenlabs.io)
The Dynamic variables docs explicitly let you “Set placeholders” in the tool UI “for testing.” If a variable isn’t replaced (name/syntax mismatch, or you’re not in a Twilio call context), the placeholder remains visible. See the Troubleshooting section to verify the variable name and {{double_curly}} syntax. (elevenlabs.io)

How to fix:

Confirm the run is an actual Twilio call (native Twilio integration or register‑call flow), not a web/simulated session. system__call_sid will only populate on Twilio calls. (elevenlabs.io)
Verify the parameter references {{system__call_sid}} exactly (case‑sensitive) and uses the Dynamic variable value type in the tool; if it isn’t replaced, the Troubleshooting checklist applies. (elevenlabs.io)
Prefer the inbound Twilio Personalization webhook: ElevenLabs sends call_sid (along with caller_id, agent_id, called_number) to your webhook during the dial phase; return it in conversation_initiation_client_data as a dynamic variable your tool can read. This avoids relying on placeholders. (elevenlabs.io)

Reference:

Dynamic variables (system__call_sid; placeholders; troubleshooting). (elevenlabs.io)
Twilio personalization (webhook receives call_sid). (elevenlabs.io)
Register Twilio calls (advanced flow). (elevenlabs.io)

light violet Mar 23, 2026, 4:50 PM

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Prefer the inbound Twilio Personalization webhook: ElevenLabs sends call_sid (along with caller_id, agent_id, called_number) to your webhook during the dial phase; return it in conversation_initiation_client_data as a dynamic variable your tool can read. This avoids relying on placeholders.

i dont get this one can you simply explain

#i used dynamic variable system__call_sid to be sent over as parameter on a webhook tool on the conv