Use Bandwindow API from Node.js: JSON POST

app.js

var https = require("https");

 function callBandWindowAPI( requestOptions, data ) {
    return new Promise((resolve, reject) => {
        var postReq = https.request(
            requestOptions,
            function(response) { // console.log('\n\nin fun...', response);
                const { statusCode } = response;
                if (statusCode >= 300) {
                    reject(
                        new Error( response.statusMessage )
                    );
                }

                const chunks = [];

                response.on('data', (chunk) => {
                    chunks.push(chunk);
                });

                response.on('end', () => {
                    const result = Buffer.concat(chunks).toString();
                    resolve( JSON.parse(result) );
                });

            }
        );

        if (data != null) {
          postReq.write( JSON.stringify(data) );
        }

        postReq.end();
    })
}

const api_host = "YOUR_ACCOUNT.shopwindow.io";
const auth_un = "YOUR_USER";
const auth_pw = "YOUR_PASSWORD";

function addPersonToGroup()
{
    callBandWindowAPI(
    {
    host: api_host,
    path: '/dg3_rpchost/Zealand/crm/DataAPI/GroupAPI/GroupAPI/addPerson',
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Basic ' + new Buffer( auth_un + ':' + auth_pw ).toString('base64')
    },
    },

    // data:
    {
        "group_id": "YOUR_GROUP_ID",
        "person_id": "YOUR_PERSON_ID"
    }

    )
    .then(
    response => {
    console.log(response);
    }
    )
    .catch(
    error => {
    console.log(error);
    }
    );
}



addPersonToGroup();

James,
Here's a tip:
Always send a JSON body in your POST, even if you have nothing to send. You can just send "{}" in that case.