First, make sure that you have the latest version of Flipd installed on your device.
For iPhones: Flipd will sound a 'ping' when your session is complete as long as your screen is off and your sound is on.
Go to your device Settings.
Scroll down and select Flipd.
Select Notifications.
Toggle Allow Notifications to ON
For Android devices (instructions may vary by device): Flipd will sound a 'ping' when your session is complete as long as your sound is on.
Go to your device Settings.
Scroll down and select Apps.
Under Downloaded, scroll down and select Flipd.
Check the box that says Show notifications