PHP Login with Dropbox issues.

Hello, im following the guide on how to use the APIs so my app can use Login with Dropbox. But im having issues getting a token.

This is my code to see why im getting the following error.

<?php

$request = new HttpRequest();
$request->setUrl('https://api.dropboxapi.com/2/auth/token/from_oauth1');
$request->setMethod(HTTP_METH_POST);

$request->setHeaders(array(
  'postman-token' => '273abf8c-7816-67c2-0949-f24bfc57383c',
  'cache-control' => 'no-cache',
  'content-type' => 'application/json',
  'authorization' => 'Basic m1qbv920v0xwxlm:xxxxxx'
));

$request->setBody('{
    "oauth1_token": "m1qbv920v0xwxlm",
    "oauth1_token_secret": "xxxxx"
}');

try {
  $response = $request->send();

  echo $response->getBody();
} catch (HttpException $ex) {
  echo $ex;
}

This is the error.

{
    "error_summary": "invalid_oauth1_token_info/.",
    "error": {
        ".tag": "invalid_oauth1_token_info"
    }
}