script.liquid

{% if event.preview %}
  {% capture order_json %}
    {
      "admin_graphql_api_id": "gid://shopify/Order/12345",
      "tags": "",
      "note_attributes": {
        {{ options.cart_attribute_to_monitor__required | json }}: "Hello!"
      }
    }
  {% endcapture %}

  {% assign order = order_json | parse_json %}
{% endif %}

{% assign order_tags = order.tags | split: ", " %}
{% assign attribute_name = options.cart_attribute_to_monitor__required %}
{% assign attribute_value = order.note_attributes[attribute_name] %}

{% if attribute_value == blank %}
  {% log "Attribute is not present" %}
{% elsif order_tags contains attribute_value %}
  {% log message: "Order is already tagged", tag: attribute_value %}
{% else %}
  {% action "shopify" %}
    mutation {
      tagsAdd(
        id: {{ order.admin_graphql_api_id | json }}
        tags: {{ attribute_value | json }}
      ) {
        userErrors {
          field
          message
        }
      }
    }
  {% endaction %}
{% endif %}