// in UE script, make sure you resolve properly the suitlet external URL:
var suitletURL = url.resolveScript({
        scriptId: 'customscript_your_suitlet_scriptid',
        deploymentId: 'customdeploy_your_suitlet_deploymentid',
        returnExternalUrl: true
});

var response = https.post({
        url : suitletURL,
        headers : myHeaders,
        body : myBody
});