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] Dynamic Variables](https://docs.retellai.com/build/dynamic-variables) [[2] Custom Function](https://docs.retellai.com/build/conversation-flow/custom-function) [[3] Custom function failure to substitute dynamic variable](https://community.retellai.com/t/custom-function-failure-to-substitute-dynamic-variable/231) [[4] Can't use dynamic variable with date-time format in GET URL for custom function?](https://discord.com/channels/1186424376300679209/1405204331896246434) ​

### Answer --- Yes, Retell supports dynamic URL parameters in custom functions. You can use the

{{variable_name}}

syntax to inject dynamic variables into your endpoint URLs. [(1) ]() Where you can use dynamic variables: - Endpoint URL (path parameters) - Query parameters - Request headers [(2) ]() Example URL with dynamic variable:

<https://api.example.com/appointments/%7B%7Bappointment_id%7D%7D>

For query parameters, you can define them in the custom function configuration, and both the description and const value can include dynamic variables. Important requirements: 1. The variable must be extracted using the Extract Dynamic Variables node before the custom function that uses it is called. [(3) ]() 2. Use double curly braces:

{{variable_name}}

not

{variable_name}

. 3. Variable names are case-sensitive and must match exactly. [(1) ]() If you're passing variables in query parameters, use the Query Parameters field in your custom function setup—Retell will automatically URL-encode these variables for the request. [(4) ]()