How to get access token using refresh token in DocuSign and PHP?

Question

I want to update my access token using the previous refresh token in DocuSign? I am getting

{
    "error": "invalid_grant",
    "error_description": "unsupported_grant_type"
}

Below is how I made the request.

$client_id = env('DOCUSIGN_CLIENT_ID');
        $client_secret = env('DOCUSIGN_CLIENT_SECRET');

        $encoded_client_id = utf8_decode(base64_encode($client_id));
        $encoded_client_secret = utf8_decode(base64_encode($client_secret));

        $integrator_and_secret_key = "Basic " . "{$encoded_client_id}:{$encoded_client_secret}";
        // $integrator_and_secret_key = "Basic " . utf8_decode(base64_encode("{$client_id}:{$client_secret}"));

        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, 'https://account-d.docusign.com/oauth/token');
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_POST, 1);
        $data = array(
            'refresh_token' => "My refresh token from previous successful request",
            'grant_type' => 'refresh_token',
        );
        curl_setopt($ch, CURLOPT_POSTFIELDS, $data);

        $headers = array();
        $headers[] = "Authorization: Basic " . "{$encoded_client_id}:{$encoded_client_secret}";
        $headers[] = 'Content-Type: application/x-www-form-urlencoded';
        $headers[] = 'Cache-Control: no-cache';
        
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

        $result = curl_exec($ch);
        if (curl_errno($ch)) {
            echo 'Error:' . curl_error($ch);
        }
        Log::info($result);

Answer 1

For those who stuck on this issue: The solution was just to change the content-type from application/x-www-form-urlencoded to application/json