Trigger to downscale mongodb from M40 to R40

MongoDB Atlas App Services & Realm Atlas Triggers & Functions
1

Hi
I am using the following code to downscale my mongodb cluster from M40 to R40 but unable to do so. I want to downscale the cluster at night time when there is lesser traffic to save the cost.

exports = async function () {

    // Supply projectID and clusterNames...
    const projectID = <projectId>;
    const clusterName = <clusterName>;

    // Get stored credentials...
    const username = <AtlasPublicKey>;
    const password =<AtlasPrivateKey>;

    // Set the desired instance size...
    const body = {
        "providerSettings": {
            "providerName": <Provider name>,
            "instanceSizeName": "R40"
        }
    };

    result = await context.functions.execute('modifyCluster', username, password, projectID, clusterName, body);
    console.log(JSON.stringify(result));

    if (result.error) {
        return result;
    }

    return clusterName + " scaled down";
};

On executing the above trigger on M40 cluster gives me following error:

{
  "detail": "The min instance size (M40) must be in the same instance family as the proposed instance size (R40).",
  "error": {
    "$numberInt": "400"
  },
  "errorCode": "COMPUTE_AUTO_SCALING_MIN_INSTANCE_SIZE_FAMILY_INVALID",
  "parameters": [
    "M40",
    "R40"
  ],
  "reason": "Bad Request"
}

If anyone can help me to achieve this downscaling activity