Getting “missing_required_parameter: ‘tools[4].function’” error when adding file search tool

[danimr]

Hi all, I’m running into this exception when trying to add a file search tool to my tool definitions.

Not sure what I’m missing here. Any ideas?

System.Exception
  HResult=0x80131500
  Message=missing_required_parameter: Missing required parameter: 'tools[4].function'.

Here’s the code I’m using:

// Define the file search tool
var fileSearchTool = new FileSearchTool();
fileSearchTool.MaxNumberResults = 20;
fileSearchTool.RankingOptions = new RankingOptions();
fileSearchTool.RankingOptions.ScoreThreshold = 1;

var fileSearchToolDefinition = ToolDefinition.DefineFileSearch(fileSearchTool);

// Add the file search tool to your tools definition list
toolsDefinition.Add(fileSearchToolDefinition);

var request = new ChatCompletionCreateRequest
{
  Messages = messages,
  Model = "gpt-4o",
  //Model = "gpt-4.1",
  MaxTokens = maxTokens,
  Temperature = 0.9f,
  ResponseFormat = responseFormat,
  Tools = toolsDefinition, 
};