I have a beard but the hair won't grow under my chin. I would like to know why and if I am able to fix it (Photo)

Facial hair growth is a genetic trait.  If you have very little facial hair there isn't much you can do to increase the growth.  A surgical option would be a hair transplant procedure.

that is a relatively small area and you would do very well with a hair transplant procedure.  It would only require a couple hundred follicular units harvested from the back of your head to get the job done. Consult with some local hair experts in your area and see what they can do for you. Good luck! 

Yes, you can try minoxidil and see if it solves the problem. Use it for a year, otherwise if you are over 25, you can have a hair transplant there