400 status: profiles is a required parameter

I’m setting up a Lambda function that will handle adding people to a List/Segment via API like in the example here: https://developers.klaviyo.com/en/reference/add-members.

Here is my snippet of code:

//url is in format of 'https://a.klaviyo.com/api/v2/list/LIST_ID/members?api_key=API_KEY'

exports.handler = async function(event) {
    console.log('Received event:', JSON.stringify(event, null, 2));

    const options = {
        method: 'POST',
        headers: {Accept: 'application/json', 'Content-Type': 'application/json'},
        body: JSON.stringify(event),
    };


    const promise = await new Promise(function(resolve, reject) {
        https.get(url, options, (res) => {
            res.on('data', (d) => {console.log('response:', d.toString())});
            resolve(res.statusCode)
          }).on('error', (e) => {
              console.log('error:', e.toString());
            reject(Error(e))
          })
        });

    console.log("HELLO?");
    console.log(promise);
    return promise

}

//results

2022-03-05T20:08:20.031Z	8f81d290-144e-4c44-a590-ad3b77f05c42	INFO	Received event: {
  "profiles": {
    "email": "george.washington@klaviyo.com"
  }
}
2022-03-05T20:08:20.276Z	8f81d290-144e-4c44-a590-ad3b77f05c42	INFO	response: {"detail":"profiles is a required parameter."}
2022-03-05T20:08:20.276Z	8f81d290-144e-4c44-a590-ad3b77f05c42	INFO	HELLO?
2022-03-05T20:08:20.277Z	8f81d290-144e-4c44-a590-ad3b77f05c42	INFO	400

I am providing input in the following format:
{
  "profiles": {
    "email": "george.washington@klaviyo.com"
  }
}
This call would work in Postman, but not on AWS lambda. Am I missing something else?