Why can't I hear when I plug in headphones?

Make sure the headphones being used are completely plugged in. The headphones being partially plugged in can cause low sound quality or no sound at all. If you are still not hearing any audio after checking the plug, try using the headphones on another device. If the same issue persists, try using a different set of headphones as they might be faulty. If audio issues continue with functional headphones and they are plugged in fully, then it is possible the headphone jack might be faulty. In this case, the headphone jack probably needs to be replaced. Amazon Fire HD 10 Troubleshooting Guide

Lick the head of the plug in and insert, for some reason the contacts are connecting very well. That did the trick.

its not working