Why isn't Messages.app text sending? [duplicate]

For starters here is my current setup:

I have an iPhone 5s and a MacBook Pro 13" mid 2012 model with OSX 10.10.4. Recently I changed the storage to an SSD and with that change I started to set up iMessage. At first iMessage worked for a decent period of time I was getting texts on time and sending them through my Mac just fine. About a week ago suddenly I couldn't send any messages without getting the "Not Delivered" and that red exclamation mark. Going through pages of forums many of the problems were either a year old or older and were very repetitive. It was either delete some files through Keychain Access, restart something or turn on the message forwarding.

Update: After playing around I realized that I can send messages to some of my contacts. These contacts are people who don't have this red highlight on their names and if they do have their name highlighted in red then I cannot send messages to them.

Update2: After looking through imessage on my mac I realized that all the contacts that I cannot send to have usually been sent through text not imessage since their text bubbles are green. The ones I can send to are blue.

I just want to know how to fix my current problem.

What you are trying to do is send SMS messages from Messages on your Mac to people without iOS devices, correct? (Just fixed this for my wife this morning.)

Be sure to add your Mac to your iPhone's Text Message Forwarding.

On your iPhone:

• Go to Settings
• Messages then select Text Message Forwarding
• There you will see a list of devices that use your Apple ID for Messages
• Add your MacBook if listed.
• Enter the code displayed on your Mac into the iPhone dialog when prompted.

Now you should be able to text from your Mac using Messages.

Apple support documentation for further reading.

I'd try signing in and out of iMessage on your Mac to see if that helps.