# Custom Function (GET) not receiving arguments from Extract Variables node

**URL:** <https://community.retellai.com/t/custom-function-get-not-receiving-arguments-from-extract-variables-node/790>\
**Category:** Support Help\
**Tags:** agent-logic\
**Created:** [February 6, 2026, 10:14am UTC](https://community.retellai.com/t/custom-function-get-not-receiving-arguments-from-extract-variables-node/790 "2026-02-06T10:14:38Z")\
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**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:** [February 6, 2026, 10:15am UTC](https://community.retellai.com/t/custom-function-get-not-receiving-arguments-from-extract-variables-node/790/2 "2026-02-06T10:15:02Z")

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Based on the documentation and community discussions, there’s a known issue with how dynamic variables work in Custom Functions with GET requests in Conversation Flow.

**The Root Cause:**

When you extract variables using the Extract Dynamic Variables node, those variables are saved to the session context[(1)](https://docs.retellai.com/build/dynamic-variables). However, for Custom Functions with GET requests, there’s a specific configuration requirement for query parameters[(2)](https://docs.retellai.com/build/conversation-flow/custom-function).

**The Solution:**

In your Custom Function’s Query Parameters section, you need to configure both the parameter description AND ensure the variable is properly referenced. Based on community troubleshooting, try this approach[(3)](https://discord.com/channels/1186424376300679209/1430715756030722149)[(4)](https://discord.com/channels/1186424376300679209/1442542149546803312):

1. In the Query Parameters section, set:

2. Make sure the Extract Variables node runs **before** your Custom Function node in the flow[(5)](https://community.retellai.com/t/custom-function-failure-to-substitute-dynamic-variable/231)

3. Verify the variable name matches exactly (case-sensitive) between extraction and usage[(5)](https://community.retellai.com/t/custom-function-failure-to-substitute-dynamic-variable/231)[(4)](https://discord.com/channels/1186424376300679209/1442542149546803312)

**Important Notes:**

- Query parameters can include dynamic variables, and there’s a switch to change between parameter description or const value[(2)](https://docs.retellai.com/build/conversation-flow/custom-function)
- Both description and const value can use dynamic variables[(2)](https://docs.retellai.com/build/conversation-flow/custom-function)
- The description will be resolved by the LLM while const value will be applied directly to the function[(2)](https://docs.retellai.com/build/conversation-flow/custom-function)

**Verification:**

After making these changes, check your call logs. You can verify if the variable was properly extracted by looking at the `collected_dynamic_variables` field in your call details[(6)](https://docs.retellai.com/api-references/get-call)[(5)](https://community.retellai.com/t/custom-function-failure-to-substitute-dynamic-variable/231).

If the issue persists after these adjustments, the call logs should show whether the variable has a value when the tool is invoked[(5)](https://community.retellai.com/t/custom-function-failure-to-substitute-dynamic-variable/231).

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_[View the full topic](https://community.retellai.com/t/custom-function-get-not-receiving-arguments-from-extract-variables-node/790)._