Hello, i use the library https://github.com/ringcentral/ringcentral-php.
$apiResponse = $rcsdk->platform()->post('/restapi/oauth/token', [ 'refresh_token' => $data['refresh_token'], 'grant_type' => 'refresh_token', 'endpoint_id' => $_ENV['RC_AppKey']
]);
I get a response from the server, Unsupported grant type. What is the problem?