I'm new to Firebase and I decided to use it on an app I'm working on. I use a PHP script to send automated push notifications. To do that, I supply the recipient's registration token along with the message itself and send it to Firebase, which will then send the push notification to the target device.
What will happen if I send a push notification to an invalid token? I believe it will fail since there's no recipient but will I get penalized for it, especially when it happens multiple times? I did some research but found nothing that mentions it.