Incoming call goes to Voicemail even when person at extention is ready to answer the call

When a new call cames for extention 300 it goes to Voicemail but the person at that extension is not busy, is properly logged qand ready to answer the call.

Please help.

This is a common thing when the extension is not registered or communicating with the server properly. Please check that the extension is properly registered and working. Also check that DND is not enabled (both at the server level and the phone level).