Facebook permission to access leads expires after weeks to months .this is completely normal and out of our control. this allows Facebook users to have better control over their data and the companies accessing that data.
We will alert you if the Facebook permission expire through email and notification .you can renew permissions by using the following steps
1. Goto settings>manage integrations >facebook >Disconnect integration
2. simply Relogin from your Facebook ads account follow the process to renew your facebook permissions .\
You can contact us at support@3sigmacrm.com if you need any help