{ "error": { "code": 400, "message": "Recipient of the message is not set.", "status": "INVALID_ARGUMENT", "details": [ { "@type": "type.googleapis.com/google.rpc.BadRequest", "fieldViolations": [ { "field": "message", "description": "Recipient of the message is not set." } ] }, { "@type": "type.googleapis.com/google.firebase.fcm.v1.FcmError", "errorCode": "INVALID_ARGUMENT" } ] } }