Yes I just managed to get it working, I spent ages trying to find out what Unified Schema meant, then simply tried passing data in as an object.
If anyone else wants to use this, code below (obviously you can pass values in event data)…
const gaEvent = {
'x-ga-measurement_id': 'UA-*********',
'v': 1,
't': 'event',
'cid': event.guid,
'ea': 'tracking',
'ec': 'serverToServer',
'el': 'Cake Conversion Failed'
};
sendEventToGoogleAnalytics(gaEvent, (response) => {
data.gtmOnFailure();
});