Any settings you've made on your device will override the settings you specify in the app. If you want Webex notifications but have notifications turned off on your device, then you won't get notified outside of the app when someone sends you a message, updates a space, or starts a meeting. So, make sure your device notifications are turned on:
iPhone and iPad:
If you have the Webex app installed on more than one device, the app detects which device you're using, or have used in the last 2 minutes, and only sends message and meeting notifications there. You're considered active in the app whenever you send messages, or read new ones.
For example, if you've been reading or sending messages at your Windows computer, and then start using the app on your Android phone, the app knows to send notifications to your phone instead of your computer. If the app doesn't detect any activity 40 seconds after it sends you a notification, then it sends the notification to all of your devices so that it reaches you on at least one.