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Out-of-Session Callback Response Guide

It often happens that Proxy receives messages and calls to Proxy numbers in your numbers pool that are not from a Participant in an Open Session. When that happens, if your Proxy Service has an Out of Session Callback Url specified, Proxy will forward that inbound payload to you, along with any information we may have as to previous Sessions for the caller/sender.

There are two types of responses you can return to customize your customer’s experience:

  1. Valid TwiML, with the Content-Type response header set to application/xml
  2. Valid Auto-create session JSON, with the Content-Type response header set to application/json


The ability to return TwiML for Programmable Voice and TwiML for Programmable SMS allows you to customize the out-of-session caller/sender experience by enabling you to respond with custom <Play>, <Say>, <Message> and other verbs.

Auto-create session JSON

If you determine, based on the information included in the callback payload, that the caller/sender should be connected to a particular Agent (Agent X), you can respond with json that tells Proxy to create a Session between the caller/sender and Agent X. Proxy will create the Session and Participants and will then proceed as if the caller/sender had reached an open Session.

Auto-Create Session Fields





The Unique Name for the Session. Should NOT include PII.



The Session mode (message-only, voice-only, or voice-and-message)

No. Based on your Participants, Proxy will try to make an intelligent choice of mode.


TTL, in seconds, after which Session should expire, if any

No. Does not default to any value.


Date/Time at which Session should expire, if any

No. Does not default to any value.


Real Phone Number of the second Participant (e.g., your agent)



Proxy Identifier to use for second Participant (e.g., a Reserved Number from your pool)

No. Proxy will choose a non-Reserved number from the pool if not specified.

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        Sample auto-create session JSON for Proxy

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