Enable SMS Forwarding between iOS 8.1 and Yosemite

No code's shown on Mac?

Me too. 

I have this solution after googling  DuckDuckGoing. 

here the excerpt 

I've found a solution on another forum and it worked for me:

Try this: Go to your iPhone Messages settings and turn off iMessages and turn it on again. Then go to the iMessages Settings on your Mac and do the same. After that it worked for me. Also make sure to activate your telephone number in the iMessages settings on your Mac.

and yeah, it works, :)