"invalid_client" error while trying to fetch token from Intuit API

Question

I'm using Curl/PHP to get the token to communicate with QuickBooks Intuit API.

I'm able to summon the following response (a JSON Text error):

{"error":"invalid_client"}

This is how:

Starting Page

$parameters = array(
    'client_id' => "my client id",
    'scope' => "com.intuit.quickbooks.accounting",
    'redirect_uri' => "http://localhost/redirect.php",
    'response_type' => "code",
    'state' => "RandomState"
);
$authorizationRequestUrl = 'https://appcenter.intuit.com/connect/oauth2?' . http_build_query($parameters);
header("Location: ".$authorizationRequestUrl);

Redirect endpoint (page) fetching access token

$queries = array();
parse_str($_SERVER['QUERY_STRING'], $queries);

$client_id = "My Sandbox client id";
$client_secret = "My Sandbox secret";
$redirect_url = "http://localhost/redirect.php";
$access_token_url = "https://oauth.platform.intuit.com/oauth2/v1/tokens/bearer";
$scope = "com.intuit.quickbooks.accounting openid profile email phone address";

$authorizationHeader = "Basic ".base64_encode($client_id.":".$client_secret);

$data = array(
    'redirect_uri' => $redirect_url,
    'grant_type' => 'authorization_code',
    "code" => $queries["code"]
);
$curl = curl_init();

curl_setopt_array($curl, array(
    CURLOPT_URL => $access_token_url,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_CUSTOMREQUEST => "POST",
    CURLOPT_POSTFIELDS => http_build_query($data),
    CURLOPT_HTTPHEADER => array(
        "Authorization" => $authorizationHeader,
        "Accept" => "application/json",
        "Content-Type" => "application/x-www-form-urlencoded",
        "Connection" => "keep-alive"
    ),
));

$response = curl_exec($curl);
print_r($response); # see JSON Text error above

How can I prevent the invalid_client error code with the QuickBooks Intuit API?

Answer 1

I just figured out the issue. I was missing the certificate file in the request. It is mandatory or we get an invalid_client error.