Firebase FCM: invalid-argument

Question

I\'m trying FCM for the first time, so just using their sample code. In fact I\'m even sending their sample messages. The following code, which is straight from the document

Answer 1

As Carlos Fernandez Sanz pointed out, one cause for this is that the client and server are connected to different firebase projects. Project name appears in the google-services.json file on the client and in the credentials json on the server.