Controller is firing but I can't get the $_GET

I changed over to POST and added
   xhr.setRequestHeader("Content-type", "application/json");
   xhr.setRequestHeader("X-Requested-With",'xmlhttprequest');

Now, I am getting this error:

[Sun Mar 25 11:57:47.099508 2018] [:error] [pid 13272:tid 1652] [client ::1:56672] PHP Deprecated:  Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php://input stream instead. in Unknown on line 0

Any ideas?

I am also getting:

background.js:85 POST http://localhost/Subit_backend/register%....com%22%7D 400 (Bad Request)

proof that an old dog can learn new tricks