add_action('rest_api_init', function(){
    register_meta( 'post', 'rank_math_focus_keyword', array( 'show_in_rest' => true, 'single' => true, 'type' => 'string', 'auth_callback' => function(){return true;} ));
    register_meta( 'post', 'rank_math_description', array( 'show_in_rest' => true, 'single' => true, 'type' => 'string', 'auth_callback' => function(){return true;} ));
});