Microsoft Graph API Error: 'Request payload cannot be null' when Creating Online Meeting"

I'm trying to create a Microsoft Teams online meeting using the Microsoft Graph API in Python. My Azure AD app has delegated permission OnlineMeetings.ReadWrite, and I'm using the /me/onlineMeetings endpoint to create the meeting. However, I keep encountering the following error:
Error: 400, {"error":{"code":"General","message":"Request payload cannot be null.","innerError":{"request-id":"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX","date":"2025-01-28T06:03:29","client-request-id":"XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"}}}

Here’s my Python code:

import requests

# Azure AD App credentials
CLIENT_ID = "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"
TENANT_ID = "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"
CLIENT_SECRET = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"

AUTHORITY = f"https://login.microsoftonline.com/{TENANT_ID}"

# User credentials
USERNAME = "XXXX@example.com"
PASSWORD = "password"


# Authentication
def get_access_token():
    data = {
        "grant_type": "password",
        "client_id": CLIENT_ID,
        "client_secret": CLIENT_SECRET,
        "scope": "https://graph.microsoft.com/.default",
        "username": USERNAME,
        "password": PASSWORD,
    }

    response = requests.post(f"{AUTHORITY}/oauth2/v2.0/token", data=data)

    if response.status_code == 200:
        return response.json().get("access_token")
    else:
        raise Exception(f"Error: {response.status_code}, {response.text}")


def create_teams_meeting():
    try:
        access_token = get_access_token()

        # Prepare the meeting data
        meeting_data = {
            "startDateTime": "2025-01-29T10:00:00",  
            "endDateTime": "2025-01-29T11:00:00",   
            "subject": "Random Meeting",
        }

        # Send the request to create the meeting
        headers = {"Authorization": f"Bearer {access_token}", "Content-Type": "application/json"}
        response = requests.post(
            "https://graph.microsoft.com/v1.0/me/onlineMeetings", 
            headers=headers, 
            json=meeting_data
        )

        if response.status_code == 201:
            meeting = response.json()
            return meeting["joinUrl"]
        else:
            raise Exception(f"Error creating meeting: {response.status_code}, {response.text}")

    except Exception as e:
        print(f"An error occurred: {e}")
        return None

What I’ve Checked:

1. Access Token: The token is being generated successfully.
2. Permissions: Verified that my Azure AD app has the OnlineMeetings.ReadWrite delegated permission and admin consent has been granted.
3. Payload: The meeting_data payload contains startDateTime, endDateTime, and subject, as per the Microsoft Graph API documentation.
4. Headers: Authorization and Content-Type headers are included in the request.: Authorization and Content-Type headers are included in the request.

The startDateTime and endDateTime fields should be in the correct ISO 8601 format, including the time zone offset.

For example:

"startDateTime": "2025-01-29T10:00:00Z",
"endDateTime": "2025-01-29T11:00:00Z"