How to send FCM to entire app using ARC : I cant find any information regarding how to target just the app, I don't have any topics and I don't want to merely target a single user.

The documentation states that a to is optional but I just receive a missingregistration error:

>This parameter specifies the recipient of a message.
>
>The value can be a device's registration token, a device group's notification key, or a single topic (prefixed with /topics/). To send to multiple topics, use the condition parameter.

This is my current setup:
https://i.stack.imgur.com/CRlVe.png

Removing the "to" field just gives me an error and the message is merely "to".