Knowledge base

Understand why your SIP calls failed

A practical guide to SIP response codes, plain-English explanations, and retry guidance for outbound calling teams using A1ROUTES.

Knowing the reason behind a failed call helps teams distinguish bad data from temporary network conditions, make smarter retry decisions, reduce wasted dialing, and improve campaign reporting.

Talk to Support Book a Voice Reliability Review

404Not FoundUsually points to invalid, incomplete, or unreachable number data.

480Temporarily UnavailableOften worth retrying later under your normal campaign logic.

503Service UnavailableUsually temporary route, provider, or destination-side capacity behavior.

580Precondition FailureA1ROUTES max outbound rate protection blocked the call.

Why this matters

Why SIP cause-code visibility matters for outbound teams

Smarter retry decisions

Know when to retry later and when to stop redialing.

Better data hygiene

Identify invalid or incomplete numbers faster.

Cleaner campaign metrics

Separate bad data from connectivity or policy issues.

Less wasted agent time

Focus effort on callable leads and viable destinations.

More confident support conversations

Share the exact failure signal when escalating with A1ROUTES.

Failure categories

Not all failed calls mean the same thing

Data / dialed-number issues

The destination may be invalid, gone, incomplete, or ambiguous.

404 Not Found410 Gone484 Address Incomplete

Temporary user or destination issues

The user, endpoint, or network may be unavailable at that moment.

408 Request Timeout480 Temporarily Unavailable486 Busy Here

Policy / auth / permission issues

Credentials, permissions, policy rules, or caller ID may need review.

401 Unauthorized403 Forbidden407 Proxy Authentication Required

Technical / media mismatch issues

The route may not accept the method, codec, SDP, or requested media.

415 Unsupported Media Type488 Not Acceptable Here

Route / provider / upstream issues

A carrier, destination, or upstream route may be temporarily unable to accept traffic.

503 Service Unavailable

A1ROUTES protection signals

Account-level controls can protect you from dialing above allowed rates.

580 Precondition Failure

Common questions

The most common codes our customers ask about

404

Not Found

Check data

A1ROUTES Softphone wording: Not Found
Meaning: The dialed number or user is usually not found by the destination network.
Retry guidance: Do not keep retrying blindly if repeated for the same number.
Suggested action: Check number format, country code, and lead-data quality.

408

Request Timeout

Retry later

A1ROUTES Softphone wording: Request Timeout
Meaning: The network did not get a timely answer from the destination side.
Retry guidance: Reasonable to retry later, especially if it is not repeated at scale.
Suggested action: Track if one destination or carrier pattern is recurring.

480

Temporarily Unavailable

Retry later

A1ROUTES Softphone wording: Temporarily Unavailable
Meaning: The user or destination is often unavailable at that moment.
Retry guidance: Retry later according to your campaign retry rules.
Suggested action: Keep it separate from invalid-number outcomes in reporting.

486

Busy Here

Retry later

A1ROUTES Softphone wording: Busy Here
Meaning: The destination endpoint is busy or rejecting because it is occupied.
Retry guidance: Retry later or follow your normal busy-call logic.
Suggested action: Do not treat it as a bad number by default.

488

Not Acceptable Here

Check config

A1ROUTES Softphone wording: Not Acceptable Here
Meaning: The destination may not accept the offered codec, SDP, or media setup.
Retry guidance: A plain retry may fail again until configuration is reviewed.
Suggested action: Ask technical support to review media and endpoint settings.

503

Service Unavailable

Retry laterEscalate if persistent

A1ROUTES Softphone wording: Service Unavailable
Meaning: The destination side, upstream carrier, or route was temporarily unable to accept the call.
Retry guidance: Often temporary. Retry later or use an alternate route if available.
Suggested action: If recurring at scale, ask A1ROUTES to review route performance.

580

Precondition Failure

Rate control

A1ROUTES Softphone wording: Precondition Failure
Meaning: A1ROUTES blocked the call because your max outbound rate threshold was hit.
Retry guidance: Do not retry until you confirm the destination rate is acceptable.
Suggested action: Review the destination and max outbound rate. See how to set maximum outbound rate.

Searchable reference

Complete SIP cause-code reference

Use the filters to focus on retry logic, data cleanup, configuration checks, escalation patterns, or A1ROUTES custom signals.

400

Bad Request

Check config

A1ROUTES Softphone wording: Bad Request

Usually means: The request was malformed or not understood.
Typical causes: Formatting, SIP header, or dial-string issue.
Retry guidance: Retry after checking format.
Next step: Review dialed number and SIP settings.
Type: Configuration issue

401

Unauthorized

Check config

A1ROUTES Softphone wording: Unauthorized

Usually means: Authentication is required or credentials were not accepted.
Typical causes: Wrong username, password, IP auth, or registration setup.
Retry guidance: Retry only after credentials are checked.
Next step: Verify SIP authentication details.
Type: Configuration issue

402

Payment Required

Top up account

A1ROUTES Softphone wording: Payment Required

Usually means: Your A1ROUTES account has run out of balance or does not have enough balance for the call.
Typical causes: Low prepaid balance, failed recharge, or billing threshold reached.
Retry guidance: Retry after topping up your account.
Next step: Check your balance and top up. See how to recharge your A1ROUTES account.
Type: Policy/rate-control issue

403

Forbidden

Check configEscalate

A1ROUTES Softphone wording: Forbidden

Usually means: The request is understood but not allowed.
Typical causes: Blocked destination, caller ID policy, permission, or account rule.
Retry guidance: Retrying the same call usually will not help.
Next step: Check permissions, KYC, caller ID, and destination rules.
Type: Policy or configuration issue

404

Not Found

Check data

A1ROUTES Softphone wording: Not Found

Usually means: The number or user was not found.
Typical causes: Invalid number, bad country code, stale lead data.
Retry guidance: Do not keep retrying blindly.
Next step: Clean or verify the number.
Type: Data issue

405

Method Not Allowed

Check config

A1ROUTES Softphone wording: Method Not Allowed

Usually means: The SIP method is not allowed by the destination or server.
Typical causes: Endpoint or proxy method restrictions.
Retry guidance: Retry after technical review.
Next step: Review SIP method and endpoint behavior.
Type: Configuration issue

406

Not Acceptable

Check config

A1ROUTES Softphone wording: Not Acceptable

Usually means: The requested response or media is not acceptable.
Typical causes: Media, header, or capability mismatch.
Retry guidance: Check configuration first.
Next step: Review endpoint and codec compatibility.
Type: Configuration issue

407

Proxy Authentication Required

Check config

A1ROUTES Softphone wording: Proxy Authentication Required

Usually means: The SIP proxy needs authentication.
Typical causes: Missing or incorrect proxy credentials.
Retry guidance: Retry after credentials are corrected.
Next step: Check proxy auth and registration settings.
Type: Configuration issue

408

Request Timeout

Retry laterEscalate if repeated

A1ROUTES Softphone wording: Request Timeout

Usually means: No timely response came back.
Typical causes: Temporary network, destination, or route delay.
Retry guidance: Retry later.
Next step: Escalate if many calls to the same destination time out.
Type: Temporary or provider-side issue

410

Gone

Check data

A1ROUTES Softphone wording: Gone

Usually means: The user or resource existed previously but is no longer available.
Typical causes: Old number, disconnected destination, stale records.
Retry guidance: Repeated retries are usually low value.
Next step: Suppress or verify the lead record.
Type: Data issue

413

Request Entity Too Large

Check config

A1ROUTES Softphone wording: Request Entity Too Large

Usually means: The SIP request body is too large.
Typical causes: Large SDP or unusual headers.
Retry guidance: Retry after endpoint review.
Next step: Ask technical support to inspect SIP messages.
Type: Configuration issue

414

Request-URI Too Long

Check configCheck data

A1ROUTES Softphone wording: Request-URI Too Long

Usually means: The dialed URI is too long or malformed.
Typical causes: Bad dial string, copied extra characters, URI formatting.
Retry guidance: Retry only after cleaning the dial string.
Next step: Review number formatting and dial plan.
Type: Data or configuration issue

415

Unsupported Media Type

Check config

A1ROUTES Softphone wording: Unsupported Media Type

Usually means: The offered media type is not supported.
Typical causes: Codec or SDP mismatch.
Retry guidance: Retry after codec settings are reviewed.
Next step: Check codec list and media configuration.
Type: Configuration issue

416

Unsupported URI Scheme

Check config

A1ROUTES Softphone wording: Unsupported URI Scheme

Usually means: The URI scheme is not supported.
Typical causes: Using an unsupported SIP URI format.
Retry guidance: Retry with corrected URI format.
Next step: Review dial plan or SIP URI construction.
Type: Configuration issue

420

Bad Extension

Check config

A1ROUTES Softphone wording: Bad Extension

Usually means: An unsupported SIP extension was required.
Typical causes: Unsupported Require header or SIP feature.
Retry guidance: Retry after changing SIP feature settings.
Next step: Review SIP headers with support.
Type: Configuration issue

421

Extension Required

Check config

A1ROUTES Softphone wording: Extension Required

Usually means: The destination requires a SIP extension not present in the request.
Typical causes: Missing SIP feature support.
Retry guidance: Retry after technical review.
Next step: Ask support whether a specific extension is required.
Type: Configuration issue

423

Interval Too Brief

Check configRetry with adjustment

A1ROUTES Softphone wording: Interval Too Brief

Usually means: A requested registration or session interval is too short.
Typical causes: Registration expiry or session timer mismatch.
Retry guidance: Retry after increasing interval settings.
Next step: Review registration/session timer values.
Type: Configuration issue

480

Temporarily Unavailable

Retry later

A1ROUTES Softphone wording: Temporarily Unavailable

Usually means: The user or destination cannot be reached right now.
Typical causes: Offline endpoint, no coverage, temporary destination state.
Retry guidance: Retry later.
Next step: Classify separately from invalid-number failures.
Type: Temporary issue

481

Call/Transaction Does Not Exist

Check config

A1ROUTES Softphone wording: Call/Transaction Does Not Exist

Usually means: The referenced call or transaction was not found.
Typical causes: Late cancel, dialog mismatch, endpoint timing issue.
Retry guidance: Usually retry the next normal call, not the same transaction.
Next step: Escalate if repeated across many calls.
Type: Temporary or configuration issue

482

Loop Detected

Check configEscalate

A1ROUTES Softphone wording: Loop Detected

Usually means: The request appears to be looping through routing paths.
Typical causes: Routing loop or misconfigured forwarding.
Retry guidance: Retrying without route changes may repeat.
Next step: Escalate routing configuration.
Type: Configuration or provider-side issue

483

Too Many Hops

Check configEscalate

A1ROUTES Softphone wording: Too Many Hops

Usually means: The request passed through too many routing points.
Typical causes: Looping route, bad forwarding, or hop limit reached.
Retry guidance: Escalate if persistent.
Next step: Ask A1ROUTES to review route path if seen at scale.
Type: Provider-side or configuration issue

484

Address Incomplete

Check data

A1ROUTES Softphone wording: Address Incomplete

Usually means: The dialed number is incomplete.
Typical causes: Missing digits, country code, area code, or prefix.
Retry guidance: Do not retry until corrected.
Next step: Normalize the number format.
Type: Data issue

485

Ambiguous

Check data

A1ROUTES Softphone wording: Ambiguous

Usually means: The destination address could match multiple targets.
Typical causes: Ambiguous dial string or routing interpretation.
Retry guidance: Retry after cleaning the dialed address.
Next step: Check number format and dial plan.
Type: Data or configuration issue

486

Busy Here

Retry later

A1ROUTES Softphone wording: Busy Here

Usually means: The user or endpoint is busy.
Typical causes: Customer is on another call or rejecting while occupied.
Retry guidance: Retry later using normal busy logic.
Next step: Do not classify as invalid number by default.
Type: Temporary issue

487

Request Terminated

Retry if appropriate

A1ROUTES Softphone wording: Request Terminated

Usually means: The call attempt was cancelled before completion.
Typical causes: Caller hung up, dialer cancelled, timeout logic.
Retry guidance: Retry if your campaign logic allows.
Next step: Check dialer timeout and agent behavior.
Type: Temporary or campaign-control issue

488

Not Acceptable Here

Check config

A1ROUTES Softphone wording: Not Acceptable Here

Usually means: The destination does not accept the offered media/session setup.
Typical causes: Codec mismatch, SDP issue, media-policy mismatch.
Retry guidance: Retry after media settings are reviewed.
Next step: Review codec and endpoint compatibility.
Type: Configuration issue

489

Bad Event

Check config

A1ROUTES Softphone wording: Bad Event

Usually means: The event package is not understood or supported.
Typical causes: Presence, subscription, or event handling mismatch.
Retry guidance: Retry after endpoint settings are reviewed.
Next step: Ask support if it affects calling flow.
Type: Configuration issue

491

Request Pending

Retry later

A1ROUTES Softphone wording: Request Pending

Usually means: Another related request is already in progress.
Typical causes: Glare or overlapping SIP re-INVITE/update behavior.
Retry guidance: Retry after a short delay.
Next step: Escalate if repeated across many calls.
Type: Temporary or configuration issue

493

Undecipherable

Check config

A1ROUTES Softphone wording: Undecipherable

Usually means: The request could not be decrypted or understood securely.
Typical causes: Encryption, certificate, or secure SIP issue.
Retry guidance: Retry after security settings are checked.
Next step: Review TLS/SRTP or secure signaling setup.
Type: Configuration issue

494

Security Agreement Required

Check config

A1ROUTES Softphone wording: Security Agreement Required

Usually means: The destination requires a SIP security agreement.
Typical causes: Security negotiation or policy mismatch.
Retry guidance: Retry after security settings are reviewed.
Next step: Escalate to technical support if persistent.
Type: Configuration issue

503

Service Unavailable

Retry laterEscalate if persistent

A1ROUTES Softphone wording: Service Unavailable

Usually means: A route, upstream carrier, or destination side was temporarily unable to accept the call.
Typical causes: Short-term congestion, maintenance, capacity limits, or brief route issue.
Retry guidance: Reasonable to retry later. Treat as temporary unless it persists.
Next step: If recurring at scale, ask A1ROUTES to review route performance.
Type: Provider-side or temporary issue

580

Precondition Failure

Rate controlReview settings

A1ROUTES Softphone wording: Precondition Failure

Usually means: A1ROUTES max outbound rate setting blocked the call.
Typical causes: The destination rate exceeded your configured allowed max rate.
Retry guidance: Do not retry until the rate and destination are reviewed.
Next step: Review rate settings or read how to set maximum outbound rate.
Type: Policy/rate-control issue

Action flow

What should I do when I see a SIP error?

1. Read the code

Capture the exact code and reason phrase.

2. Classify it

Decide whether it looks like data, temporary, config, or provider behavior.

3. Choose action

Retry, clean the number, change settings, or escalate.

4. Improve logic

Feed the outcome back into campaign retry rules and reporting.

404

Likely bad data

Do not keep retrying blindly.

480

Temporary

Retry later.

486

Busy

Use normal busy logic.

503

Route/provider

Retry later; escalate if recurring.

580

Rate control

Review max outbound rate settings.

A1ROUTES advantage

Why A1ROUTES customers benefit from cause-code transparency

Typical low-visibility setup

Failed call but no real reason
Agents keep redialing bad numbers
Managers misread answer-rate metrics
Support conversations start from guesswork

A1ROUTES transparency

Failure reason becomes clearer
Teams make smarter retry decisions
Bad data and route issues separate better
Cleaner reporting and campaign optimization
Less wasted dialing and support friction

A1ROUTES softphone

Using the A1ROUTES softphone?

If you use the A1ROUTES Softphone, the call status often reflects the SIP reason phrase returned by the network. This page helps translate those statuses into plain-English actions for your team.

A1ROUTES Softphone status486 Busy Here

MeaningDestination busy

Next stepRetry later

Where SIP cause-code visibility helps most

Support

Need help interpreting repeated SIP failures?

If your team is seeing recurring 404s, 480s, 486s, 503s, or max-rate blocks, A1ROUTES can help review your call patterns, retry logic, and route behavior.

Contact A1ROUTES Support Book a Voice Reliability Review

Share the exact SIP code and destination

Include timestamp, caller ID, and dialed number pattern

Separate repeated bad data from route-level patterns

Ask for route review when issues repeat at scale