Invalid input: Expected an object type but received None instead.

The "400 Bad Request" error with the specific message "None is not of type 'object' - 'messages.2'" in the OpenAI API is likely due to several possible reasons:

Invalid Request Payload

The error indicates that the JSON payload sent in the request is not valid. Specifically, it suggests that the messages array contains an element that is None or null, which is not an object as expected by the API.

Incorrect Message Format

The API expects each message in the messages array to be a valid object with specific properties. If any message in the array is missing required fields or has an incorrect format, it can trigger this error.

Deprecation of Certain Fields

The error could also be related to deprecated fields, such as function_call being None or null in the message object. This can cause the API to reject the request because it expects a different structure.

API Validation

Recent changes or updates to the API might include stricter validation rules, such as checking the type and structure of each element in the request payload more rigorously, leading to this error if the request does not meet the new criteria.