When I text to international contacts, it's red and can't send message

I am using imessages on my macbook air. I am trying to add an international contact, so I do it, trying to get the most basic info. When I go into contacts, the phone number has like a red circle with a horizontal white line going through it.

So I ignore it and try to text. I hover over it, and its green, When I text, its red and I cant send a message. I heard that messages can send SMS to Androids, so I try that again, but nothing is working.

Hover = Green

Text = Red

why and how to solve this?