Receiver issue may include below phenomena:

No sound from the receiver;
Low sound issue;
Receiver Sound quality - Sound quality is abnormal;

1. Check if the receiver produces no sound, low sound or sound quality issues occur during a phone call or during voice calls via Skype, Facebook etc.
2. If the receiver is clogged or dirty, it will not work. Make sure the receiver is not blocked by a protective case or protective film.
3. During the call, please turn on the speaker. If you still can not hear sound, there may be a problem with the network or cell reception. Please try again later or try calling from a different location with a good network if possible.
4. Restart the device to check if the issue persists.

If the issue only occurs when using a 3rd party app, please uninstall or check the latest update.