> ## Documentation Index > Fetch the complete documentation index at: https://developers.telnyx.com/llms.txt > Use this file to discover all available pages before exploring further. # SIP Response Codes > Reference of SIP response codes you'll see on Telnyx SIP Trunking calls — 4xx client errors, 5xx server errors, 6xx global failures, and what they mean. Telnyx-specific SIP response codes for diagnosing call failures. ## D-Series Codes (4XX Responses) Client-side errors related to account configuration, limits, and permissions. ### D1X: Account & Connection Issues | Code | SIP Status | Description | Resolution | | ------- | ---------- | -------------------------------------------------- | --------------------------------------------------------------- | | D1 | 403 | Concurrent outbound calls exceed global limit | Reduce active calls or increase limit in outbound voice profile | | D10-D17 | 403 | Connection, profile, or account disabled/forbidden | Verify SIP connection and outbound voice profile are active | | D18 | 404 | SIP connection inactive | Enable the SIP connection | | D19 | 404 | Account blocked (billing) | Review account balance and payment method | ### D2X: Profile & Channel Limits | Code | SIP Status | Description | Resolution | | ------- | ---------- | ---------------------------------------------------- | ---------------------------------------------- | | D2 | 403 | Outbound profile concurrent call limit exceeded | Reduce active calls or increase profile limit | | D21 | 480 | No destination/forwarding number associated | Verify destination number is valid and active | | D22 | 403 | Channel limit exceeded (DID, connection, or profile) | Check channel allocations | | D24 | 403 | Rate per minute exceeds profile maximum | Adjust rate limits in outbound voice profile | | D25-D29 | 403 | Authentication or connection validation failed | Verify SIP credentials and connection settings | ### D3X: Connection & URI Issues | Code | SIP Status | Description | Resolution | | ------- | ---------- | ------------------------------------------------ | ------------------------------------------------ | | D3 | 403 | Connection concurrent call limit exceeded | Reduce active calls or increase connection limit | | D30-D31 | 403 | Invalid SIP URI or subdomain | Verify SIP URI format and subdomain settings | | D35 | 403 | Invalid caller ID format | Use E.164 format (e.g., +12125551234) | | D36 | 403 | Using another account's DID as caller ID | Use only assigned phone numbers | | D38 | 403 | No outbound voice profile assigned to connection | Assign an outbound voice profile | ### D4X: Routing & Destination Issues | Code | SIP Status | Description | Resolution | | ---- | ---------- | ------------------------------------------ | -------------------------------------------- | | D40 | 404 | Destination exists but no route available | Verify destination and routing configuration | | D41 | 403 | Dialed prefix forbidden (fraud prevention) | Contact support to enable destination | | D42 | 405 | SIP REFER not allowed | Enable call transfer in connection settings | | D49 | 403 | NANPA origination number lacks valid LRN | Ensure phone number has LRN data | ### D5X: Channel Billing & Verification | Code | SIP Status | Description | Resolution | | ------- | ---------- | ------------------------------------------ | ---------------------------------------- | | D5 | 486 | Legacy channel billing limit exceeded | Review channel billing settings | | D51 | 403 | Non-Telnyx number not verified | Use Verified Numbers API | | D52-D54 | 403 | Restricted origination number | Verify number ownership and status | | D56 | 486 | Global channel billing limit exceeded | Contact support | | D57 | 403 | HD voice disabled for phone number | Enable HD voice in phone number settings | | D59 | 404 | Special/short number unsupported by region | Use supported number type | ### D6X: Account Tier Restrictions | Code | SIP Status | Description | Resolution | | ------- | ---------- | -------------------------------------- | -------------------------------------- | | D60-D61 | 403 | Account tier requires verified numbers | Upgrade account tier or verify numbers | | D63 | 403 | Number port pending | Wait for port completion | | D64-D65 | 403 | Regulatory requirement pending | Complete regulatory documentation | ### D7X, D8X, D9X: Additional Restrictions | Code | SIP Status | Description | Resolution | | ---- | ---------- | -------------------------------------------- | ------------------------------------- | | D7 | 403 | No outbound voice profile assigned | Assign an outbound voice profile | | D8 | 404 | Missing E911 caller ID | Configure E911 caller ID | | D9 | 403 | International destination rate limit reached | Review rate limits or contact support | ## P-Series Codes (Protocol Issues) SIP protocol violations or proxy-level issues. ### P0X: Protocol Violations | Code | SIP Status | Description | Resolution | | ------- | ---------- | ---------------------------------------- | ----------------------------------------------- | | P01 | 403 | Invalid Request-URI (proxy anycast IP) | Use correct contact header | | P02 | 403 | CANCEL without matching INVITE | Only send CANCEL for active INVITE transactions | | P04 | 403 | REGISTER with To tag (RFC non-compliant) | Remove To tag from REGISTER requests | | P05-P06 | 403 | CPS limit or message size exceeded | Reduce call rate or message size | | P14-P16 | 403 | Contact header length violation | Shorten contact header to under 512 bytes | | P18 | 403 | Empty destination in Request-URI or To | Include valid destination in SIP headers | | P29 | 500 | REGISTER processing failure | Retry registration or contact support | | P51 | 403 | Contact header exceeds 512 bytes | Reduce contact header length | | P81-P83 | 403 | Username validation issues | Verify SIP username format | | P93 | 403 | Hop count exceeded | Check for routing loops | ## R-Series Codes (Registration & Authentication) SIP registration and authentication issues. | Code | SIP Status | Description | Resolution | | ------- | ---------- | ------------------------------------------- | ---------------------------------------------- | | R14 | 403 | Empty authentication username | Provide valid SIP username | | R16-R18 | 403 | Invalid/short/mismatched username | Use alphanumeric username matching credentials | | R47 | 403 | Multiple Contact addresses in REGISTER | Register one contact address per request | | RG1 | 480 | User not registered (credential connection) | Register SIP client before making calls | ## Routing & Media Codes ### PE-Series: Routing Failures | Code | SIP Status | Description | Resolution | | ------- | ---------- | --------------- | ------------------------------- | | PE1-PE6 | 503 | No routes found | Verify destination is reachable | ### T-Series: Termination Issues | Code | SIP Status | Description | Resolution | | ---- | ---------- | ------------------------------------ | ------------------------------------- | | TV1 | 503 | Downstream carrier termination issue | Retry call or use alternative routing | | TM1 | 403 | No rates for destination prefix | Contact support about coverage | ### B-Series: Media Issues | Code | SIP Status | Description | Resolution | | ---- | ---------- | ---------------------------------------- | -------------------------------------------------- | | B3 | 488 | SRTP mismatch - encrypted media expected | Enable SRTP in SIP client or disable in connection | ## 488 Not Acceptable Media Media negotiation failures: | Scenario | Resolution | | ------------------------ | -------------------------------- | | Private IP in SDP | Use public IP addresses | | T.38 fax mismatch | Verify T.38 settings match | | IPv6 media addresses | Use IPv4 (IPv6 not supported) | | Unsupported codecs | Use G.711, G.722, G.729, or Opus | | SDP encryption conflicts | Ensure consistent SRTP settings |