$url2 = 'https://watson-api-explorer.mybluemix.net/personality-insights/api/v3/profile?raw_scores=false&csv_headers=false&consumption_preferences=true&version=2017-02-01';
$request_headers = array();
$request_headers[] = 'Accept: application/json';
$request_headers[] = 'Content-Type: text/plain';

$request_headers[] = 'Content-Language: en';
$request_headers[] = 'Accept-Language: en';

$simple_data = 'some really interesting text goes here';


$plain_data = json_encode($data);
$ch2 = curl_init( $url2 );
curl_setopt_array( $ch2, array(
    CURLOPT_POST => 1,
    CURLOPT_POSTFIELDS => $simple_data,
    CURLOPT_FOLLOWLOCATION => 1,
    CURLOPT_HEADER => $request_headers,
    CURLOPT_RETURNTRANSFER => 1,
    CURLOPT_USERPWD => 'XXX:YYY' //removed for illustration
)
);
$response2 = curl_exec( $ch2 );
var_dump($response2);

{"code":415,"sub_code":"S00002","error":"Unsupported Content-Type: "application/x-www-form-urlencoded""}