What it means
A request refers to a dialog or transaction the far end has no record of. Often a BYE or re-INVITE for a call the other side already considers dead.
SIP/2.0 481 Call/Transaction Does Not Exist
Common causes
- A BYE sent for a call the far end already tore down
- Stale dialog state after a restart or timeout
- A race where one side ended the call first
- Mismatched To or From tags
How to fix it
- Confirm both sides agree the call is still up before sending mid-dialog requests
- Check for a server restart that dropped dialog state
- Inspect the To and From tags for a mismatch
See it in your own trace
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