The Retell Community is where innovators, call center leaders, and AI enthusiasts come together to share ideas, learn best practices, and explore the future of voice automation. Join to connect with peers, get early access to product updates, and collaborate on building human-like AI voice experiences that transform customer service.

Retell AI

<@1145576664366055464> With the call_inbound, we set dynamic variables.

{
  "call_inbound": {
    "dynamic_variables": {
       "user_id": "1",
       "user_name": "Ciaran Jones",....
    }
  }
}

In functions, can I pass in the user_id?

Thanks for tagging me <@142232205832355840>. I'll look through relevant sources and get back to you shortly.

### Answer
 

---

Yes, you can pass `user_id` into custom functions. Dynamic variables set via the inbound webhook can be used in several places within custom function configurations:
[(1) ](<https://docs.retellai.com/build/dynamic-variables>)

**In the endpoint URL:**
```
<https://your-api.com/users/%7B%7Buser_id%7D%7D/action>
```
[(2) ](<https://docs.retellai.com/build/single-multi-prompt/custom-function>)

**In query parameters:**
You can define query parameters with dynamic variables—both the description and const value can include dynamic variables like `{{user_id}}`.


**In request headers:**
Header values can be static or include dynamic variables.


**In the request body (JSON schema) :**
You can use the `const` field to inject the dynamic variable:
```json
{
  "type": "object",
  "properties": {
    "user_id": {
      "type": "string",
      "const": "{{user_id}}"
    }
  }
}
```


**Important:** All dynamic variable values must be strings. If you're passing booleans or numbers, convert them to strings (e.g., `"1"` instead of `1`, `"false"` instead of `false`) .
[(1) ](<https://docs.retellai.com/build/dynamic-variables>) , [(3) ](<https://discord.com/channels/1186424376300679209/1419725903918923920>)

​
To learn more, see the sources I considered:

[[1] Dynamic Variables](https://docs.retellai.com/build/dynamic-variables)
[[2] Integrate any system with custom function](https://docs.retellai.com/build/single-multi-prompt/custom-function)
[[3] Dynamic Variables From Inbound Webhook Not Passed to the Call](https://discord.com/channels/1186424376300679209/1419725903918923920)
​

Feel free to tag <@1145576664366055464> with additional questions. I also appreciate feedback, it helps me improve.