Header format
- A valid DID associated with the Telnyx SIP connection
- In E.164 format (e.g.,
+15551234567) - Wrapped in SIP URI format
Use cases
- Multiple DIDs on a single SIP connection
- Call detail record (CDR) attribution per DID
- Billing and usage tracking per number
- Carrier-side call routing based on originating number
Requirements
- Telnyx SIP connection configured for outbound calling
- Valid DID ownership and assignment to the connection
- PBX access to modify dialplan or trunk configuration
Troubleshooting
| Issue | Solution |
|---|---|
| Header not appearing in SIP INVITE | Verify dialplan reload completed successfully |
| Call rejected by Telnyx | Confirm DID is associated with the SIP connection |
| Wrong number in header | Check variable substitution in dynamic configurations |
| FreePBX updates overwrite config | Use extensions_custom.conf to persist changes |
Alternative identification methods
For connections sharing authentication credentials:| Method | Description |
|---|---|
| P-Charge-Info header | SIP header identifying billing number |
| Tech prefix | 4-digit identifier prepended to destination |
| IP authentication token | Token-based connection validation |