# I need to receive calls using 3cx as telephony system

**URL:** <https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435>\
**Category:** Support Help\
**Created:** [January 14, 2026, 9:51am UTC](https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435 "2026-01-14T09:51:30Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Pelayo\_Garcia](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/pelayo_garcia/32/396_2.png) [@Pelayo\_Garcia](https://community.retellai.com/u/Pelayo_Garcia)\
**Post date:** [January 14, 2026, 9:51am UTC](https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435/1 "2026-01-14T09:51:30Z")

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I am trying to receive calls using 3cx as my telephony system. I have already set up a trung pointing to sip.retell.ai but I get Call or Registration to 112@(Ln.10001@Retell) has failed. sip:84.235.227.5:5060;lr replied: Not Found (404) Seems like retell is not finding my agent.

Its not a connection issue as I have been able to connect to retell but I get connected to a russian speaking ai agent.

Any details on how to proceed?

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<div class="post-metadata">

**Author:** ![support2](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/support2/32/15_2.png) [@support2](https://community.retellai.com/u/support2)\
**Post date:** [January 14, 2026, 9:51am UTC](https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435/2 "2026-01-14T09:51:53Z")

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Based on the 404 error you’re receiving, the issue is that Retell cannot route your inbound call to the correct agent[(1)](https://docs.retellai.com/deploy/custom-telephony). When using Elastic SIP Trunking with 3CX, you need to import your phone number into Retell and bind it to a specific agent[(1)](https://docs.retellai.com/deploy/custom-telephony).

## Steps to Fix This Issue

### 1. Import Your Number into Retell

You need to import your phone number in E.164 format (including country code, no spaces or special characters)[(2)](https://www.retellai.com/blog/integrating-ai-with-sip-trunking-and-modern-telephony). During import, you’ll provide:

- The termination URI to identify your elastic SIP trunk (used for outbound calls)[(2)](https://www.retellai.com/blog/integrating-ai-with-sip-trunking-and-modern-telephony)
- A unique agent ID to bind the number, ensuring inbound calls are automatically directed to the specified agent[(2)](https://www.retellai.com/blog/integrating-ai-with-sip-trunking-and-modern-telephony)
- Optional username and password for SIP trunk authentication[(2)](https://www.retellai.com/blog/integrating-ai-with-sip-trunking-and-modern-telephony)

### 2. Configure Your SIP Trunk Settings

For your 3CX trunk pointing to `sip:sip.retellai.com`, ensure you’re using the correct transport method[(1)](https://docs.retellai.com/deploy/custom-telephony):

- TCP (Recommended): `sip:sip.retellai.com;transport=tcp`[(1)](https://docs.retellai.com/deploy/custom-telephony)
- UDP: `sip:sip.retellai.com;transport=udp`[(1)](https://docs.retellai.com/deploy/custom-telephony)
- TLS: `sip:sip.retellai.com;transport=tls`[(1)](https://docs.retellai.com/deploy/custom-telephony)

You can whitelist Retell’s IP blocks in 3CX[(1)](https://docs.retellai.com/deploy/custom-telephony):

- All regions: `18.98.16.120/30`[(1)](https://docs.retellai.com/deploy/custom-telephony)
- Certain US traffic: `143.223.88.0/21`, `161.115.160.0/19`[(1)](https://docs.retellai.com/deploy/custom-telephony)

### 3. Verify Origination Settings

Check your origination (inbound) settings in your SIP trunk configuration[(1)](https://docs.retellai.com/deploy/custom-telephony). The Russian-speaking agent you’re reaching suggests calls are connecting to Retell but not routing to your specific agent because the number isn’t properly imported and bound[(1)](https://docs.retellai.com/deploy/custom-telephony).

Without importing your number and binding it to your agent, Retell cannot determine which agent should handle the inbound call, resulting in the 404 error or routing to a default/incorrect agent[(1)](https://docs.retellai.com/deploy/custom-telephony).

For additional support with your specific 3CX configuration:

- Visit [Contact Sales](https://retellai.octolane.com/)
- Ask questions on [Discord](https://discord.com/invite/wxtjkjj2zp)
- Visit [https://github.com/RetellAI/](https://github.com/RetellAI/)

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<div class="post-metadata">

**Author:** ![Pelayo\_Garcia](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/pelayo_garcia/32/396_2.png) [@Pelayo\_Garcia](https://community.retellai.com/u/Pelayo_Garcia)\
**Post date:** [January 14, 2026, 10:12am UTC](https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435/3 "2026-01-14T10:12:53Z")

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How can I inform to retell of the binded phone number from 3cx?

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<div class="post-metadata">

**Author:** ![support2](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/support2/32/15_2.png) [@support2](https://community.retellai.com/u/support2)\
**Post date:** [January 14, 2026, 10:13am UTC](https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435/4 "2026-01-14T10:13:28Z")

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To inform Retell about your phone number from 3CX, you need to use the **Import Phone Number API** [(1)](https://docs.retellai.com/api-references/import-phone-number). This binds your 3CX number to a specific Retell agent[(1)](https://docs.retellai.com/api-references/import-phone-number).

## Using the API to Import Your Number

Here’s the code to import your phone number[(1)](https://docs.retellai.com/api-references/import-phone-number):

```javascript
import Retell from 'retell-sdk';
const client = new Retell({
 apiKey: 'YOUR_RETELL_API_KEY',
});
const phoneNumberResponse = await client.phoneNumber.import({
 phone_number: '+14157774444',
 termination_uri: 'someuri.pstn.twilio.com',
});
console.log(phoneNumberResponse.inbound_agent_id);

```

[(1)](https://docs.retellai.com/api-references/import-phone-number)

## Required Parameters

When importing your 3CX number, you must provide[(1)](https://docs.retellai.com/api-references/import-phone-number):

- **phone\_number** : Your number in E.164 format (e.g., `"+14157774444"`)[(1)](https://docs.retellai.com/api-references/import-phone-number)
- **termination\_uri** : The termination URI to uniquely identify your elastic SIP trunk (used for outbound calls)[(1)](https://docs.retellai.com/api-references/import-phone-number)

## Optional Parameters to Bind Your Agent

To ensure inbound calls route to your specific agent, include[(1)](https://docs.retellai.com/api-references/import-phone-number):

- **inbound\_agent\_id** : Unique ID of the agent to bind to the number for receiving inbound calls[(1)](https://docs.retellai.com/api-references/import-phone-number)
- **outbound\_agent\_id** : Unique ID of the agent for conducting outbound calls[(1)](https://docs.retellai.com/api-references/import-phone-number)
- **sip\_trunk\_auth\_username** : Username for SIP trunk authentication[(1)](https://docs.retellai.com/api-references/import-phone-number)
- **sip\_trunk\_auth\_password** : Password for SIP trunk authentication[(1)](https://docs.retellai.com/api-references/import-phone-number)

## Complete Example with Agent Binding

```javascript
const phoneNumberResponse = await client.phoneNumber.import({
 phone_number: '+14157774444',
 termination_uri: 'someuri.pstn.twilio.com',
 inbound_agent_id: 'oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD',
 outbound_agent_id: 'oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD',
 sip_trunk_auth_username: 'username',
 sip_trunk_auth_password: '123456',
});

```

[(1)](https://docs.retellai.com/api-references/import-phone-number)

Once imported, your 3CX number will automatically use the bound agent when receiving inbound calls[(1)](https://docs.retellai.com/api-references/import-phone-number). This should resolve the 404 error you’re experiencing, as Retell will now know which agent to route calls to[(2)](https://docs.retellai.com/deploy/custom-telephony).

\*\*

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<div class="post-metadata">

**Author:** ![Pelayo\_Garcia](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/pelayo_garcia/32/396_2.png) [@Pelayo\_Garcia](https://community.retellai.com/u/Pelayo_Garcia)\
**Post date:** [January 14, 2026, 12:07pm UTC](https://community.retellai.com/t/i-need-to-receive-calls-using-3cx-as-telephony-system/435/5 "2026-01-14T12:07:37Z")

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> [@support2](#):
>
> your 3CX number will automatically use the bound agent when receiving inbound calls[(1)](https://docs.retellai.com/api-references/import-phone-number). This should resolve the 404 error you’re experiencing, as Retell will now know which agent to route calls to[(2)](https://docs.retellai.com/deploy/custom-telephony).

This has been already done. The agent is binded to a phone number but when the call is routed I am afraid I am forwarded to another agent. Is there something I need to add to my call so retell is able to know my from number?