Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

​ To learn more, see the sources I considered: [[1] LLM WebSocket](https://docs.retellai.com/api-references/llm-websocket) [[2] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[3] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) ​

### Answer When using a custom LLM and transferring calls to destinations with IVR systems, you can navigate the IVR by sending DTMF tones (digit presses) through the LLM WebSocket. [(1) ]() To press digits after a transfer, use the

digit_to_press

field in your response events. This field allows you to send DTMF tones after the content associated with that response is fully spoken. Here's how to implement it in your custom LLM responses: For **response events**: - Set

digit_to_press

to the input digit or digits you want to send - Note that you probably don't want the voice agent to speak anything when pressing digits For **agent interrupt events**: - Similarly, you can include

digit_to_press

to send DTMF tones after the interrupt content is fully spoken The

digit_to_press

field accepts digits 0-9, '*', and '#'. [(2) ]() [(3) ]() Keep in mind that when using warm transfers specifically, you can also provide a "Navigate IVR" prompt to help the agent navigate if the transfer target is an IVR system.

### Answer When using

digit_to_press

with a custom LLM, the digit is pressed after the content associated with that response is fully spoken. [(1) ]() If the IVR navigation isn't working, here are key troubleshooting steps: 1. Ensure Content is Empty or Minimal The

digit_to_press

field sends DTMF tones after content is spoken. If you want immediate digit pressing without the agent speaking, set

content

to an empty string

""

. 2. Verify Response Event Structure In your LLM WebSocket response event, ensure you're structuring it correctly: - `response_type`:

"response"

- `response_id`: matching the request - `content`:

""

(empty for no speech) - `content_complete`:

true

- `digit_to_press`: the digit(s) to press (e.g.,

"2"

) 3. Known Limitation for Post-Transfer IVR Based on community discussions, there's a known limitation: IVR navigation after a warm transfer is not currently supported. [(2) ]() The Press Digit functionality works for outbound calls where the AI agent encounters an IVR system directly, but not for navigating an IVR after transferring the call to another number that has an IVR. If you're trying to navigate an IVR post-transfer, this is on the roadmap but not yet available. The workaround would be to have your AI agent make the outbound call directly to the IVR-enabled number and navigate it before any transfer occurs.

​ To learn more, see the sources I considered: [[1] LLM WebSocket](https://docs.retellai.com/api-references/llm-websocket) [[2] IVR navigation assistance](https://discord.com/channels/1186424376300679209/1311341427665534998) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

### Answer Based on the available documentation, there's a fundamental limitation with your approach: IVR navigation after a call transfer is not currently supported. [(1) ]() The Press Digit functionality works specifically for outbound calls where the AI agent encounters an IVR system directly, not for navigating an IVR after transferring the call to another number. [(2) ]() [(1) ]() According to community discussions, when users attempted to transfer a call to an IVR-enabled number and then navigate it, the feature did not work as expected. This capability is on the roadmap but not yet available. [(1) ]() Why your code isn't working: The

digit_to_press

field in the LLM WebSocket is designed to send DTMF tones after content is fully spoken during the active call session. [(3) ]() However, when you execute a

transfer_number

, the call context changes—the AI agent is no longer actively managing the call in the same way, so the digit press doesn't occur at the right time or in the right call leg. Potential workarounds: 1. **Direct outbound calls**: Instead of transferring, have your AI agent make the outbound call directly to the IVR-enabled number and navigate it before any transfer occurs. [(1) ]() 2. **Warm transfer with extension**: For some telephony providers like Twilio, you can include the extension as part of the dial string using

sendDigits

. [(4) ]() However, this requires custom

telephony integration and isn't directly supported through Retell's transfer_number parameter. The beeping you're hearing suggests the transfer is completing, but the digit press isn't being sent to the transferred call leg—which aligns with the known limitation.

​ To learn more, see the sources I considered: [[1] IVR navigation assistance](https://discord.com/channels/1186424376300679209/1311341427665534998) [[2] Press digit (IVR navigation)](https://docs.retellai.com/build/single-multi-prompt/press-digit) [[3] LLM WebSocket](https://docs.retellai.com/api-references/llm-websocket) [[4] Hi I want to transfer a call to an extension to an extension so phoneNumber](https://discord.com/channels/1186424376300679209/1302835833551851540) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

### Answer Based on the current documentation, navigating an IVR after a warm transfer is not supported when using Custom LLM integration. [(1) ]() The

digit_to_press

functionality works for outbound calls where the AI agent directly encounters an IVR, but not for post-transfer IVR navigation. [(2) ]() [(1) ]() Available options for your scenario: 1. Use Transfer Extension Parameter For warm transfers, you can set the transfer number extension if the IVR system supports extensions. [(3) ]() [(4) ]() This allows you to automatically navigate to a specific option:

python
yield ResponseResponse(
    response_id=request.response_id,
    content="",
    content_complete=True,
    transfer_number=agency_numbers.get(self.agency) ,
    transfer_number_extension="1#",  # Extension must be 0-9, '*', '#'
    show_transferee_as_caller=True,
)

The extension must consist of digits 0-9, '*', or '#' (e.g., "123#") . 2. Configure Navigate IVR in Warm Transfer Settings For warm transfers (non-agentic) , you can provide a "Navigate IVR" prompt to help navigate if the transfer target is an IVR system. However, this setting is configured at the agent level in the dashboard, not through the Custom LLM WebSocket. 3. Custom Telephony Implementation If neither option works for your use case, you would need to handle the transfer and IVR navigation through your own telephony provider logic, as mentioned in the community discussion. [(1) ]() With Custom LLM integration, you don't have direct access to Retell's transfer call feature controls, [(5) ]() so implementing custom transfer logic with your telephony provider may be necessary. [(6) ]() The limitation you're experiencing—where the call transfers but the digit isn't pressed—is a known gap in the current Custom LLM integration. [(1) ]() **

​ To learn more, see the sources I considered: [[1] IVR navigation assistance](https://discord.com/channels/1186424376300679209/1311341427665534998) [[2] Press digit (IVR navigation)](https://docs.retellai.com/build/single-multi-prompt/press-digit) [[3] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[4] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[5] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[6] Discord message from @killianzoldeck on 2026-04-24](https://discord.com/channels/1186424376300679209/1186462578310910112/1497385864433635479) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

### Answer Based on the available sources, warm transfer is not directly supported in Custom LLM integrations. [(1) ]() When using Custom LLM via the LLM WebSocket, you can only perform cold transfers by setting the

transfer_number

field in your response event. [(2) ]() A community discussion confirms that warm transfers (three-way bridging, hold music, and human detection) remain unavailable for Custom LLM integrations. [(1) ]() The suggested workaround is to simulate a warm transfer client-side by: 1. Sending a pre-transfer message from your custom LLM before triggering the transfer 2. Then setting

transfer_number

in the response event to perform a cold transfer For reference, here's the cold transfer structure in your response event: [(2) ]()

python
yield ResponseResponse(
    response_id=request.response_id,
    content="",
    content_complete=True,
    transfer_number="+1234567890",
    show_transferee_as_caller=True,
)

The

show_transferee_as_caller

field controls how the caller ID appears to the next agent. [(1) ]() If you need true warm transfer capabilities (where the AI agent stays on the line during transfer) , you would need to use Retell's built-in agent frameworks (Single Prompt or Conversation Flow) instead of Custom LLM integration. [(3) ]()

​ To learn more, see the sources I considered: [[1] Phone transfer with custom LLM](https://discord.com/channels/1186424376300679209/1395018119050952825) [[2] LLM WebSocket](https://docs.retellai.com/api-references/llm-websocket) [[3] Keep AI Agent on the Line During Warm Transfer](https://community.retellai.com/t/keep-ai-agent-on-the-line-during-warm-transfer/173) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.