For iPhone, please ensure that the power saving mode is not on. Also check the link: https://www.easeus.com/ios-tips/notification-not-working-in-ios-11.html
If the problem persists, please write to us at support@myclassboard.in
For Android, there could be phone model specific issues, please check them here: Device Settings
There could be several other reasons for not receiving notifications. Please check here for device specific issues
Push notifications require an active Internet (data) connection. Your device must have a connection to broadband (3G, 4G, or LTE) network, or a WiFi network. Many corporate WiFi networks impose restrictions or proxy servers that can interfere with your device’s connection to the Internet.