Node JS google cloud messaging topic with prefix got Error:主题名称格式错误[duplicate]

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没有前缀,一切正常,但当我试图添加前缀,我得到“错误:主题名称格式错误”

app.post('/notify', (request, response) => {
// console.log(request.body);
var message = {
    android: {
        ttl: 3600 * 1000, // 1 hour in milliseconds
        priority: 'normal',
        notification: {
            title: request.body.fullname + ' want to join',
            body: 'email: ' + request.body.email + '; tel: ' + request.body.no_telp,
            icon: 'stock_ticker_update',
            color: '#0088aa'
        },
        data: request.body
    },
    topic: '/register/guest'
};

admin.messaging().send(message)
.then((res) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', res);
    response.send("success");
})
.catch((error) => {
    console.log('Error sending message:', error);
    response.send('error');
});

})