Persistent Menu does not work in messenger channel

Hello , please help me .
persistent menu does not work in my bot.

Thanks.
This is my code in conf

“persistentMenu”: true,
“persistentMenuItems”: [
{
“title”: “Home”,
“type”: “nested”,
“call_to_actions”: [
{
“title”: “Pay Bill”,
“type”: “postback”,
“payload”: “PAYBILL_PAYLOAD”
},
{
“type”: “web_url”,
“title”: “Latest News”,
“url”: “https://www.messenger.com/”,
“webview_height_ratio”: “full”
}
]
},
{
“title”: “Newsletter”,
“type”: “nested”,
“call_to_actions”: [
{
“title”: “Subscribe”,
“type”: “postback”,
“webview_height_ratio”: “full”,
“payload”: “SUB_NEWSLETTER”
},
{
“type”: “web_url”,
“title”: “Unsubscribe”,
“url”: “https://www.messenger.com/”,
“webview_height_ratio”: “full”,
“payload”: “UNSUB_NEWSLETTER”
}
]
},
{
“title”: “Q&A”,
“type”: “web_url”,
“url”: “https://www.messenger.com/
}
],