Freeze one failed call and one directional control
Record the Sinch product, application keys by role, number, timestamp and timezone, direction, region, termination result, origination result, call ID, callback result if used, customer-edge receipt, PBX response, answer and media. A working customer-to-Sinch termination call bounds one application, credential and egress path; it does not prove the separately configured origination application or its number assignment.
Redact application secrets, telephone numbers, addresses, callback bodies and call content. Do not move a credential or broaden a route before locating the earliest mismatch.
Prove the origination application and destination
For a static trunk, confirm the number is assigned to the intended origination application and preserve its SIP-forwarding URI. Resolve any {number} substitution and compare the resulting Request-URI, host, port and transport with the receiving PBX. For Callback API control, preserve the Incoming Call Event, call ID, application response and ConnectSIP destination.
An application that authenticates termination can coexist with a different application that owns origination. A callback event, forwarding rule and customer SIP route are three different observations.
Join Sinch evidence to the customer edge
Correlate the Sinch call ID, UTC timestamp and CDR result or reason with DNS, firewall and packet evidence at the customer edge. If Sinch generated no customer-facing attempt, investigate application assignment, forwarding or callback response. If an INVITE reached the edge, preserve its source, destination, transport, Request-URI, To, response and owning PBX object.
Use the current documented SIP and RTP ranges for the selected region as dated inputs. Do not pin one resolved edge or treat a successful signaling allowlist as a media rule.
Inspect loaded PBX identification and routing
For FreePBX, compare the GUI trunk and inbound route with generated PJSIP configuration and loaded endpoint, identify, context and dialplan state. For hand-managed Asterisk, compare the configured endpoint and identify sections with the running objects. Preserve the first divergence before editing.
A visible object is not proof that the process loaded it or selected it for this source. Do not enable anonymous SIP or an unrestricted catch-all route to make one attempt pass.
Separate TLS, SDP and RTP failures
If signaling uses TLS, verify the regional hostname, Let's Encrypt chain, local trust store, negotiated TLS version and cipher, then preserve the SIP dialog. Inspect the offer and answer for codec and SRTP agreement. Finally compare advertised and observed RTP endpoints and both packet directions.
Configured TLS is not a handshake; a completed SIP dialog is not decoded audio; an open media-port range is not two-way RTP. Correct the earliest demonstrated boundary, repeat the same call, verify answer and two-way audio, then restore temporary diagnostics.
Record limits and close the incident
Preserve the corrected application relationship, forwarding or callback state, PBX object, firewall revision, call ID, CDR, SIP result and media result. Note whether the change affects only new calls and whether a rollback was exercised.
The reviewed public material does not establish one universal retry matrix, failover timer, restoration interval or established-call survival result. No Sinch account, application, callback endpoint, PBX, firewall, packet, CDR, media stream or live call was inspected for this diagnostic.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- Sinch Voice API SIP Trunking reference ↗
- Sinch Voice API callback reference ↗
- Sinch Voice API authentication reference ↗
- Sinch Voice API call headers ↗
- Sinch Voice API call detail records ↗
- Sinch Voice API release notes ↗
- Sinch Elastic SIP Trunking product overview ↗
- Sinch BYOC SIP Trunking overview ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.