The 400 status error in the Azure OpenAI API with the message "Invalid value for 'tool_choice': 'tool_choice' is only allowed when 'tools' are specified" is occurring because the tool_choice parameter is being used without specifying the necessary tools in the request. Here are the key reasons:

• The tool_choice parameter requires that the tools field be present in the request, as it needs to know which tools to choose from.

• If the tools field is missing, the API cannot process the tool_choice parameter correctly, leading to the "Invalid value" error.

This error indicates a mismatch between the request parameters and the API's expectations regarding the tool_choice and tools fields.