<div id="remain">0</div>

$(document).on('msoptionsprice_product_action', function (e, action, form, response) {
       $('#remain').innerText = response.modification.count;   
});

<p class="msoptionsprice-count msoptionsprice-[[*id]] numeric-value" id="ajax-container">[[+count]]</p>

document.addEventListener("DOMContentLoaded", function() {
  function handleAjax() {
    const numericElements = document.querySelectorAll(".numeric-value");
    for (let i = 0; i < numericElements.length; i++) {
      const value = parseFloat(numericElements[i].textContent);
      if (value === 0) {
        numericElements[i].textContent = "Нет в наличии";
      } else if (value > 0) {
        numericElements[i].textContent = "Есть в наличии";
      }
    }
  }
  document.addEventListener("ajaxLoad", handleAjax);
  setTimeout(function() {
    const newNumericValue = document.createElement("span");
    newNumericValue.textContent = "0";
    newNumericValue.classList.add("numeric-value");
    document.body.appendChild(newNumericValue);
    const newNumericValue2 = document.createElement("span");
    newNumericValue2.textContent = "10";
    newNumericValue2.classList.add("numeric-value");
    document.body.appendChild(newNumericValue2);
    const ajaxLoadEvent = new Event("ajaxLoad");
    document.dispatchEvent(ajaxLoadEvent);
  }, 3000);
  const observer = new MutationObserver(function(mutationsList) {
    for (const mutation of mutationsList) {
      if (mutation.type === "childList") {
        const ajaxLoadEvent = new Event("ajaxLoad");
        document.dispatchEvent(ajaxLoadEvent);
      }
    }
  });
  const ajaxContainer = document.querySelector("#ajax-container");
  if (ajaxContainer) {
    observer.observe(ajaxContainer, { childList: true });
  }
});

[[!msOptionsPrice.modification?
&tpl=`count_tpl`
&where=`{"count" > 0}`
&toPlaceholder=`mycounts`
]]

[[+count]] шт

<span class="msoptionsprice-count msoptionsprice-[[*id]]">[[+mycounts]]</span>

public function createOrder()
    {
        $ms2 = $this->modx->getService('minishop2');
        $ms2->initialize('web');

        if (empty($ms2->cart->get())) {
            $this->logging->writeLog('Orderformhandler::createOrder', 'Не добавлен ни один курс.');
            return array('success' => false, 'message' => 'Не добавлен ни один курс');
        }

        $ms2->order->config['json_response'] = true;
        $ms2->order->add('receiver', $this->data['fullname']);
        $ms2->order->add('phone', $this->data['phone']);
        $ms2->order->add('delivery', $this->data['delivery']);
        $ms2->order->add('payment', $this->data['payment']);
        $ms2->order->add('region', $this->data['state']);
        $ms2->order->add('city', ($this->data['city'] ?: $this->data['state']));
        $ms2->order->add('index', $this->data['zip']);
        $response = $ms2->order->submit();

        $this->logging->writeLog('Orderformhandler::createOrder', 'Заказ успешно создан.', $response);

        if ($response['order_id']) {
            $newName = $this->base_path . $this->logdir . $response['order_id'] . '.txt';
            rename($this->logpath, $newName);
            unlink($this->logpath);
            $this->logging->logpath = $newName;
        }

        return $response;
    }