API : https://fcm.googleapis.com/v1/%7B+parent%7D/messages:send

Request body

{
    "message": {
        "registration_ids": [
            "DEVICE_TOKEN_1",
            "DEVICE_TOKEN_2"
        ],
        "notification": {
            "title": "postman test 2",
            "body": "New news story available."
        },
        "data": {
            "type": "refresh"
        }
    }
}

I have tried multiple things in place of “Tokens” but none of them worked
“registration_ids” , “to” , “Token” etc key name tried but getting error like below,

{
    "error": {
        "code": 400,
        "message": "Invalid JSON payload received. Unknown name "Tokens" at 'message': Cannot find field.",
        "status": "INVALID_ARGUMENT",
        "details": [
            {
                "@type": "type.googleapis.com/google.rpc.BadRequest",
                "fieldViolations": [
                    {
                        "field": "message",
                        "description": "Invalid JSON payload received. Unknown name "Tokens" at 'message': Cannot find field."
                    }
                ]
            }
        ]
    }
}

Can Anyone tell me how to send push notification to multiple devices with FCM token ??