Error in call to API function "auth/token/from_oauth1": Bad HTTP "Content-Type" header: "application

i am calling app auth api but i am receiving below error.

Error in call to API function "auth/token/from_oauth1": Bad HTTP "Content-Type" header: "application/json; boundary=------------------------796cea680fa095ca". Expecting one of "application/json", "application/json; charset=utf-8", "text/plain; charset=dropbox-cors-hack".

Code

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://api.dropboxapi.com/2/auth/token/from_oauth1");
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'POST');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: application/json',
    'Authorization: Basic bmF0dWdweTsdwqegzbnE1MDFs4OnFiN3F3an3p3anpkdGJzOA=='
));
curl_setopt($ch, CURLOPT_POSTFIELDS, array(
    'oauth1_token' => 'natugpy83123nq5sdf01l',
    'oauth1_token_secret' => 'qb7qwjsdfzwjzdtfbs8',
));
$result = curl_exec($ch);
curl_close($ch);