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Transfer call



Transfer a call to a new destination. If the transfer is unsuccessful, a 'call_hangup' webhook will be sent indicating that the transfer could not be completed. The original call will remain active and may be issued additional commands, potentially transfering the call to an alternate destination.

Expected Webhooks:

  • Call initiated
  • Call bridged to Leg B
  • You will receive either a Call answered](/docs/api/v1/call-control/Call%20Webhooks#call-answered) webhook or a [Call hangup webhook.
  • Answering Machine Detection Result if answering_machine_detection set to detect, greeting_end or detect_words.
  • Answering Machine Greeting Ended if answering_machine_detection set to greeting_end or detect_words and machine detected initially.


Path Parameters

    call_control_id stringrequired

    Unique identifier and token for controlling the call



    to stringrequired

    The DID or SIP URI to dial out and bridge to the given call.

    from string

    The 'from' number to be used as the caller id presented to the destination ('to' number). The number should be in +E164 format. This attribute will default to the 'from' number of the original call if omitted.

    audio_url string

    Audio URL to be played back when the transfer destination answers before bridging the call. The URL can point to either a WAV or MP3 file.

    timeout int32

    Default value: 30

    The number of seconds that Telnyx will wait for the call to be answered by the destination to which it is being transferred. If the timeout is reached before an answer is received, the call will hangup and a 'call_hangup' webhook with a 'hangup_cause' of 'timeout' will be sent. Minimum value is 5 seconds. Maximum value is 120 seconds.

    time_limit int32

    Default value: 14400

    Sets the maximum duration of a Call Control Leg in seconds. If the time limit is reached, the call will hangup and a 'call_hangup' webhook with a 'hangup_cause' of 'time_limit' will be sent. For example, by setting a time limit of 120 seconds, a Call Leg will be automatically terminated two minutes after being answered. The default time limit is 14400 seconds or 4 hours and this is also the maximum allowed call length.

    answering_machine_detection string

    Possible values: [detect, detect_beep, detect_words, greeting_end, disabled]

    Default value: disabled

    Enables Answering Machine Detection. When a call is answered, Telnyx runs real-time detection to determine if it was picked up by a human or a machine and sends an 'answering_machine_detection_result' webhook with the analysis result. If 'greeting_end' or 'detect_words' is used and a 'machine' is detected, you will receive another 'amd_greeting_ended' webhook when the answering machine greeting ends with a beep or silence. If detect_beep is used, you will only receive 'amd_greeting_ended' if a beep is detected.



    Optional configuration parameters to modify 'answering_machine_detection' performance.

    total_analysis_time_millis int32

    Default value: 3500

    Maximum timeout threshold for overall detection.

    after_greeting_silence_millis int32

    Default value: 800

    Silence duration threshold after a greeting message or voice for it be considered human.

    between_words_silence_millis int32

    Default value: 50

    Maximum threshold for silence between words.

    greeting_duration_millis int32

    Default value: 3500

    Maximum threshold of a human greeting. If greeting longer than this value, considered machine.

    initial_silence_millis int32

    Default value: 3500

    If initial silence duration is greater than this value, consider it a machine.

    maximum_number_of_words int32

    Default value: 5

    If number of detected words is greater than this value, consder it a machine.

    maximum_word_length_millis int32

    Default value: 3500

    If a single word lasts longer than this threshold, consider it a machine.

    silence_threshold int32

    Default value: 256

    Minimum noise threshold for any analysis.

    greeting_total_analysis_time_millis int32

    Default value: 5000

    If machine already detected, maximum timeout threshold to determine the end of the machine greeting.

    greeting_silence_duration_millis int32

    Default value: 1500

    If machine already detected, maximum threshold for silence between words. If exceeded, the greeting is considered ended.



    Custom headers to be added to the SIP INVITE.

  • Array [

  • name stringrequired

    The name of the header to add.

    value stringrequired

    The value of the header.

  • ]

  • client_state string

    Use this field to add state to every subsequent webhook. It must be a valid Base-64 encoded string.

    target_leg_client_state string

    Use this field to add state to every subsequent webhook for the new leg. It must be a valid Base-64 encoded string.

    command_id string

    Use this field to avoid duplicate commands. Telnyx will ignore commands with the same "command_id".

    sip_auth_username string

    SIP Authentication username used for SIP challenges.

    sip_auth_password string

    SIP Authentication password used for SIP challenges.


200: Successful response


    result stringrequired

422: Error response


    code stringrequired
    title stringrequired
    detail stringrequired