I was already checking other threads with the same error and still couldn't fix it.

So here is my PHP code:

$data = [
        "client_id" => "id-here",
        "client_secret" => "secret-here",
        "refresh_token" => "refresh-token-here",
        "grant_type" => "refresh_token"
    ];
    $ch = curl_init( 'https://www.googleapis.com/oauth2/v4/token' );
    curl_setopt( $ch, CURLOPT_HTTPHEADER, array('Content-Type:application/x-www-form-urlencoded'));
    curl_setopt( $ch, CURLOPT_POSTFIELDS, $data );
    curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );

    $result = curl_exec($ch);
    curl_close($ch);

    dd($result);

As you can see I do have the "application/x-www-form-urlencoded" included, yet I still get a response:

{
  "error": "unsupported_grant_type",
  "error_description": "Invalid grant_type: "
}

I hope that someone will be able to help. Any tips, links, or code-snippets will do! Thank you!