If your HTC M9 isn't charging, there are a few potential reasons why. Here are some troubleshooting tips to help you figure out what's causing the issue and how to fix it.
One common reason why phones don't charge is because the charging port is dirty or obstructed. Check your phone's charging port for any debris or buildup that could be preventing the charger from making a good connection. If you see anything, use a can of compressed air to blow it out, or use a cotton swab to gently clean the area.
Another possibility is that your charger is not working properly. Try plugging your phone into a different outlet or using a different USB cable to see if that makes a difference. If you're still having trouble, try using a different power adapter (if you have one).
It's also possible that there's an issue with your phone's battery. If your phone won't hold a charge or charges very slowly, it might be time for a new battery. You can usually get this replaced by taking it to an authorized HTC service center.
If none of these troubleshooting tips fix the problem, then it's likely that there is a more serious hardware issue with your phone and it will need to be repaired or replaced by HTC.