If you've turned on notifications in the Osper app but aren't receiving them, you may need to adjust your phone's settings.
Android
Open your phone's settings.
Scroll down and tap App - Osper.
Select the option to show notifications.
iOS
Open your iPhone's settings app, scroll down and tap Notifications.
Tap Osper, then turn on the settings to Allow Notifications.
Click below for more information on Google and Apple support
https://support.google.com/nexus/answer/6111294?hl=en-GB
https://support.apple.com/en-gb/HT201925