Manii

Go to your Grand Theft Auto V folder main directory.  Right Below your RagePluginHook.exe is your Rage Hook Log Text file.  A new one is created every time you play the game.  Do Ctrl A to copy log, now come to this thread.  You see that "EYE ICON" near the font size when you are replying to this message.  Its called a "Spoiler" Paste it in there with Ctrl P.   

Now,  for the help.  A few things can be going on with Vocal Dispatch.  With this file comes a nice Document that will guide you through the proper sayings.  Now its very important to note that you must have a proper mic installed.  Make sure you have somewhat of a decent one.   Speak clearly directly into the mic.  

Few examples

"Request Code 3 back up"
"Request Air Support"

Now in my video below,  it really doesn't matter much what you say into the mic,  it only wants to hear key words.  So if I say "Dispatch Ocean 21, Requesting Air Unit"  it will only detect "Requesting Air Unit"

These are after I press Right Alt.  Not sure to be honest if it matters if its Right Alt or Left Alt,  probably does not matter.  Are you hearing the small tone after you press Alt?  I would guess so as you are getting a "Didn't copy".  But try what I mentioned.  Try out your mic in different areas as well to make sure people can hear you first.  

Not that my YouTube video will help but you can hear how I speak clearly into the mic

Hope any of this helps