$response = $client->request('POST', 'http://httpbin.org/post', [ 'form_params' => [ 'field_name' => 'abc', 'other_field' => '123', 'nested_field' => [ 'nested' => 'hello' ] ] ]);
use GuzzleHttp\Client; $client = new Client(); $response = $client->post('url', [ GuzzleHttp\RequestOptions::JSON => ['foo' => 'bar'] // or 'json' => [...] ]);