Steps to Fix it:
- Drag the Ringer and Alerts slider back and forth a few times in Settings > Sounds (or Settings > Sounds & Haptics). If you don't hear anything or the speaker button on the Ringer and Alerts slider is darkened, your speaker may need to be repaired.
- Go to Notifications > Settings>Scroll down to Messages and check that sounds are turned on. and the box is marked with a green checkmark. Also, ensure sure your ringer is not set to silent; if it is, the top switch on the left side of your iPhone will be red, indicating that your ringer is turned off.
- Choose the App you want to switch on Delivery for. Off quietly...
- To turn them back on, tap and tick Lock Screen and/or Banners.
- If Badges isn't turned on, turn it on.
- If you want to hear your notification, choose a sound from the Sounds menu.
Read More: How to manage apps from your iPhone X Storage menu?
