### Answer Retell AI doesn't have a dedicated health check or test endpoint specifically documented in the official sources. However, you can implement monitoring using these approaches: For Testing Webhooks: You can test your webhook endpoint locally before deploying [(1) ]() . The setup guide shows you can use tools like Postman or CURL to send test webhook payloads to your endpoint :

bash
curl --location 'localhost:8080/webhook' \
--header 'Content-Type: application/json' \
--data '{
 "event": "call_ended",
 "call": {
 "call_type": "phone_call",
 "from_number": "+12137771234",
 "to_number": "+12137771235",
 "direction": "inbound",
 "call_id": "Jabr9TXYYJHfvl6Syypi88rdAHYHmcq6",
 "agent_id": "oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD",
 "call_status": "registered",
 "metadata": {},
 "retell_llm_dynamic_variables": {
 "customer_name": "John Doe"
 },
 "start_timestamp": 1714608475945,
 "end_timestamp": 1714608491736,
 "disconnection_reason": "user_hangup",
 "transcript": "...",
 "opt_out_sensitive_data_storage": false
 }
}'

For Monitoring Calls: You can register a phone call and monitor its status using the Register Phone Call API [(2) ]() and then retrieve call details with the Get Call API [(3) ]() . The

call_status

field will show you if calls are working (

registered

,

ongoing

,

ended

, or

error

) [(3) ]() [(2) ]() . Webhook Reliability: Retell's webhooks have a 10-second timeout and will retry up to 3 times if they don't receive a success status (2xx) [(4) ]() . Webhooks are triggered in order but are non-blocking . For comprehensive monitoring, you could create a test call periodically and check if your webhook receives the expected events (

call_started

,

call_ended

,

call_analyzed

) .

​ To learn more, see the sources I considered: [[1] Setup guide](https://docs.retellai.com/features/register-webhook) [[2] Register Phone Call](https://docs.retellai.com/api-references/register-phone-call) [[3] Get Call](https://docs.retellai.com/api-references/get-call) [[4] Webhook Overview](https://docs.retellai.com/features/webhook-overview) ​

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

### Answer According to a Discord discussion, Retell's billing policies charge 10 seconds for calls that are not connected [(1) ]() . The exact cost depends on your agent settings and whatever the LLM of your agent costs per 10 seconds . If you're using SIP trunking, you would be charged the platform + LLM fee for the 10 seconds, but not the telephony fee . For the most accurate and up-to-date billing information, I recommend checking your Retell dashboard or contacting Retell support directly, as billing policies may have been updated since this discussion.

​ To learn more, see the sources I considered: [[1] Discord message from @sxnvddxct on 2025-03-07](https://discord.com/channels/1186424376300679209/1186462578310910112/1347375210135027836) ​

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

### Answer To determine if a call reached voicemail, check the

call_analysis

object in the call response. Specifically, look for the

in_voicemail

field [(1) ]() . Here's the structure:

json
"call_analysis": {
  "call_summary": "The agent called the user to ask question about his purchase inquiry...",
  "in_voicemail": false,
  "user_sentiment": "Positive",
  "call_successful": true,
  "custom_analysis_data": {}
}

The

in_voicemail

boolean field indicates whether the call reached a voicemail . This field is available in the call analysis data after the call ends . Additionally, you can check the

disconnection_reason

field - if it equals

"voicemail_reached"

, that also indicates the call went to voicemail . The call analysis becomes available after you receive the

call_analyzed

webhook event .

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] Update Call](https://docs.retellai.com/api-references/update-call) ​

### Answer Based on the documentation, Retell AI will not populate custom post-call analysis fields for calls that were not connected or where no conversation took place [(1) ]() . You should check whether the

call_analysis

field exists before using it . Common reasons you might not receive call analysis: 1. Call didn't connect - If the call has a disconnection reason like

dial_failed

,

dial_no_answer

, or

dial_busy

, the

call_started

webhook won't be triggered, though

call_ended

and

call_analyzed

webhooks will still fire [(2) ]() . 2. No conversation occurred - If there was no actual conversation during the call, the analysis fields won't be populated [(1) ]() . 3. Webhook configuration - Make sure your webhook is configured to receive the

call_analyzed

event. The default webhook events for voice agents are

call_started

,

call_ended

, and

call_analyzed

[(2) ]() . You can filter which events are delivered using the

webhook_events

field when creating or updating an agent . How to access call analysis when available: You can retrieve analysis results through three methods [(1) ]() : - Dashboard - View in the history tab under "Conversation Analysis" column - Webhook - Receive real-time notifications when the

call_analyzed

event fires [(1) ]() [(2) ]() - API - Use the Get Call API to retrieve the

call_analysis

field programmatically [(1) ](

mption) [(3) ]() The

call_analysis

object contains fields like

call_summary

,

in_voicemail

,

user_sentiment

,

call_successful

, and

custom_analysis_data

[(3) ]() . If you're still not receiving analysis for calls that should have it, verify that your webhook endpoint is correctly configured and returning a success status (2xx) within the 10-second timeout [(2) ]() .

​ To learn more, see the sources I considered: [[1] Consume the analysis data](https://docs.retellai.com/features/post-call-analysis-consumption) [[2] Webhook Overview](https://docs.retellai.com/features/webhook-overview) [[3] Get Call](https://docs.retellai.com/api-references/get-call) ​

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

### Answer To test your webhook endpoint, you can test it locally before deploying [(1) ]() . Test with CURL: Use this command to send a test webhook payload to your endpoint :

bash
curl --location 'localhost:8080/webhook' \
--header 'Content-Type: application/json' \
--data '{
 "event": "call_ended",
 "call": {
 "call_type": "phone_call",
 "from_number": "+12137771234",
 "to_number": "+12137771235",
 "direction": "inbound",
 "call_id": "Jabr9TXYYJHfvl6Syypi88rdAHYHmcq6",
 "agent_id": "oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD",
 "call_status": "registered",
 "metadata": {},
 "retell_llm_dynamic_variables": {
 "customer_name": "John Doe"
 },
 "start_timestamp": 1714608475945,
 "end_timestamp": 1714608491736,
 "disconnection_reason": "user_hangup",
 "transcript": "...",
 "opt_out_sensitive_data_storage": false
 }
}'

Test with Postman: You can also use Postman to send the same JSON payload to your local endpoint . Make your endpoint online: Once local testing works, deploy your endpoint using Ngrok to make it accessible online : 1. Install ngrok:

brew install ngrok/ngrok/ngrok

2. Start ngrok: `ngrok http 3. Use the generated URL (e.g., ` as your webhook endpoint Live testing: After registering your webhook endpoint, start a web call in the dashboard to verify the webhook is triggered correctly .

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] Setup guide](https://docs.retellai.com/features/register-webhook) ​

### Answer The screeching sound and hold behavior issues you're experiencing during call transfers are likely related to your transfer configuration. Here's what you should check: For the screeching sound: When using warm transfer, configure the on-hold music setting properly [(1) ]() [(2) ]() . The default is a standard ringtone, but you have several options including Ringtone, Relaxing Sound, Uplifting Beats, or No Music [(3) ]() . The screech might be caused by audio feedback or improper hold music configuration during the transfer handoff. For the hold behavior issue: The AI agent doesn't automatically "hold" during transfers in the way you might expect [(2) ]() . When the call transfer node executes, the agent will not speak while in this node . If you want the agent to say something like "Let me transfer you right away" before performing the actual transfer, you need to put a conversation node (with

skip response

turned on) before the transfer node . Key transfer settings to configure: 1. Enable human detection - This ensures the agent checks if a human is present after the transfer target answers [(1) ]() [(2) ]() 2. Auto-greet - If enabled, the agent will immediately say "Hello" when the transfer target picks up, which encourages a response and increases the likelihood of detecting a human 3. Whisper message - A message spoken privately to the transfer target before connecting them to the original caller

4. Agent detection timeout - The maximum time the AI agent will wait to determine whether the transfer target is a human For warm transfers specifically, the original caller hears the configured on-hold music while the transfer is being processed [(2) ]() [(3) ]() . Make sure your warm transfer settings are properly configured to avoid audio issues during the handoff.

​ To learn more, see the sources I considered: [[1] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[2] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[3] Warm Transfer vs Cold Transfer - The AI Advantage in Call Centers | Retell AI](https://www.retellai.com/blog/effortless-handoffs-with-retell-ais-warm-transfer-feature) ​

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