cURL Output in PHP - php

Question

I have this curl output where I replace with my id, secret and url. It gives correct response.
curl -XPOST -H "Cache-Control:no-cache" -H "Content-Type:application/json" --user 'id:secret' 'url'
But when I'm trying to write it in php in the following way, it's giving error for invalid cleint. How to rewrite curl from the above output in the same way in php? Thanks!
$url = 'https://test.api.neteller.com/v1/oauth2/token?grant_type=client_credentials';
$clientId = 'client_id;
$clientSecret = 'secret_id';
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_USERPWD, $clientId . ":" . $clientSecret);
curl_setopt($curl, CURLOPT_HEADER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($curl);
curl_close($curl);
It's giving error - 'invalid cleint', but when I run it in console, it returns access token. This code is only for access token, not for payment.
Edited: My current code is:
$url ='https://test.api.neteller.com/v1/oauth2/token?grant_type=client_credentials';
$clientId = NETELLER_CLIENT_ID;
$clientSecret = NETELLER_CLIENT_SECRET;
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_HEADER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
$headers = array(
'Authorization: Basic '. base64_encode($clientId) . ':' . base64_encode($clientSecret),
'Content-Type:application/json'
);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
$response = curl_exec($curl);
if (curl_error($curl)) {
curl_close($curl);
throw new \Exception('System error. Can not get neteller token');
}
curl_close($curl);

Answer 1

Tried to add the credentials as part of the headers.
$headers = array(
'Authorization: Basic '. base64_encode($clientID . ':' . $clientSecret),
'Content-Type:application/json'
);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);

Answer 2

Ok I found out.
Update:
There are 4 reasons why you may get { "error": "invalid_client" } when trying to run your code.
You are using client_id + client_secret from your test account on the production environment or vice versa.
Your client_id or client_secret values are wrong.
The IP address from which your application is making outgoing requests is not white-listed in your merchant account.
You are not sending the Authorization header properly.
You missed curl_setopt($curl, CURLOPT_HTTPHEADER, array("Content-Type:application/json", "Cache-Control:no-cache")); from your code.