### Answer The LLM determines when to call the function and extracts the required parameters based on your parameter definition. [(1) ]() To configure parameters for a custom function node: Define Parameters Using JSON Schema For POST, PATCH, and PUT requests, define parameters using JSON schema format. Here's an example:

json
{
 "type": "object",
 "required": [
 "order_id"
 ],
 "properties": {
 "name": {
 "type": "object",
 "description": "",
 "properties": {
 "first_name": {
 "type": "string",
 "description": "User first name"
 },
 "last_name": {
 "type": "string",
 "const": "{{last_name}}"
 }
 }
 },
 "order_id": {
 "type": "number",
 "const": 1234
 }
 }
}

Key Points: - You can use

"description"

for the LLM to resolve the value dynamically - You can use

"const"

to apply a value directly to the function - Both description and const value can include dynamic variables using

{{variable_name}}

format Common Issues: - Ensure you add

"type": "object"

at the top level of your JSON schema - For dynamic variables in URLs or query parameters, use double curly braces:

{{variable_name}}

[(2) ]() [(3) ]() - Variables must be extracted before the function call that uses them [(3) ]() Update Node Instruction Guide the LLM on when to use the function in your node's prompt instruction. [(4) ]() For example:

​ To learn more, see the sources I considered: [[1] Custom Function](https://docs.retellai.com/build/conversation-flow/custom-function) [[2] Issue with Global Variables Not Passing in Query Parameters for Custom Function Tool](https://community.retellai.com/t/issue-with-global-variables-not-passing-in-query-parameters-for-custom-function-tool/773) [[3] Custom function failure to substitute dynamic variable](https://community.retellai.com/t/custom-function-failure-to-substitute-dynamic-variable/231) [[4] Node Functions](https://docs.retellai.com/build/conversation-flow/conversation-node-functions) ​

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