Text Message Forwarding on MacBook Air

It seemed that after I downloaded the newest update for my MacBook Air I was unable to send text messages, I can send iMessages fine by not text messages. When I went into the message settings to turn of the message forwarding and turn it back on, the code that is supposed to come up on the MacBook Air is not coming up so I can put it into my phone for text message forwarding. Can anyone help me solve this problem?