CODE EXAMPLE FOR PHP

php js

function pp_check_reactapp_ajax() {

    $request = new WP_REST_Request( 'POST', '/wp/v2/posts' );
    $request->set_header( 'content-type', 'application/json' );
    $request->set_body( '{
            "title": "'. $_POST['title'] .'"
        }');

    $response = rest_do_request( $request );

    $server = rest_get_server();
    $data = $server->response_to_data( $response, false );

    if($data['id']){
        echo '{"success": '. json_encode($data) .'}';
    } else {
        echo '{"error": "'. $data['message'] .'"}';
    }

    wp_die();

}
add_action( 'wp_ajax_nopriv_pp_check_reactapp_ajax', 'pp_check_reactapp_ajax' );
add_action( 'wp_ajax_pp_check_reactapp_ajax', 'pp_check_reactapp_ajax' );