I have no sound, only a blinking screen.
The volume of iPhone and iPad alerts have to set in the device settings (go to sound or general -> sounds) and set the volume slider on the top. The default volume for iPad is zero.
If you see this icon:
you've disabled the audio alert, click on the icon to reenable it.
If your device is muted or sound level is zero, then the alert is muted: check your mute switch and the device volume.
If you have no alert when the app is in background: check in notfication -> anchor that the sound switch is on.
If none of this helped, please contact us and we'll solve the issue.