Error message whenever I try to log into my Apple ID account
I am trying to set up my imessage on my macbook air (it used to be set up but automatically disabled) but it keeps sending an error message whenever I try to log into my apple ID account. I changed my password from my iPhone 6s and still it will not work to sign on to imessage. I can sign into icloud just fine. I have gotten into the imessage screen but nothing will sync because it will not allow me to add my phone number in my preferences and will not activate my icloud apple ID to receive messages like on my phone. I've tried updating my software, changing my password, deleting files, everything from this website: https://www.hawkdive.com/imessage-activation-error-occured-mac/
I don't want to have to go to an Apple store. Please help.
[Re-Titled by Moderator]
MacBook Air 13", OS X 10.11