Firebase push notifications always arrive as an empty message - firebase

Question

I have been trying to get push notifications working using firebase. So far I have got as far as successfully sending an empty message "tickle". The problem is adding the message payload seems to have no affect on what the client receives. That is the service worker just sees it as another empty message.
I started by going through googles guide here - https://developers.google.com/web/ilt/pwa/introduction-to-push-notifications
After going through how to send an empty message it says the message payload must be encrypted and suggests using an existing library to do it. To quote - "As with anything related to encryption, it's usually easier to use an actively maintained library than to write your own code".
I tried to use web-push-php which is one of the libraries recommended by googles guide. After having trouble with that i discovered web-php-push doesn't actually support firebase.
Looking on here i find examples that look really simple and don't event encrypt the message payload. It is simply sent in plain json. Doing this has no affect and the receiving end still thinks it's an empty message. See my code below.
I am at a complete loss with this and i'm confused why googles guide says the message data must be encrypted but there are countless examples on SO where it is just send in plain json text.
This is what i am posting from my server to the end point.
POST https://fcm.googleapis.com/fcm/send Authorization: key=[my server
key] Content-Type: application/json {"priority":10,"to":"[subscriber
id]","notification":{"body":"test body","title":"test title"}}
Here is my event listener in my service-worker.js
self.addEventListener('push', function(e) {
var body;
if (e.data) {
body = e.data.text();
} else {
body = "No message "+JSON.stringify(e);
}
var options = {
body: body
};
e.waitUntil(
self.registration.showNotification('Launtel Residential', options)
);
});
When i run the post request above the push notification occurs and triggers the service worker 'push' event as expected but no message data is present. e.data returns null. The 'e' object always just contains a flag set to true. e.isTrusted==true