Packing slips doesn't support rich text fields via the `| metafield_tag` just yet, this parses the rich text JSON into usable HTML

rich-text-parser.liquid

{% assign parsed_content = order.metafields.namespace.key | json_parse %}

{% for item in parsed_content.children %}
  {% case item.type %}
    {% when 'paragraph' %}
      <p>
        {% for child in item.children %}
          {% if child.bold and child.italic %}
            <strong><em>{{ child.value }}</em></strong>
          {% elsif child.bold %}
            <strong>{{ child.value }}</strong>
          {% elsif child.italic %}
            <em>{{ child.value }}</em>
          {% else %}
            {{ child.value }}
          {% endif %}
        {% endfor %}
      </p>
      
    {% when 'heading' %}
      {% assign heading_size = 'h' | append: item.level %}
      <{{ heading_size }}>
        {% for child in item.children %}
          <span {% if child.italic %}style="font-style: italic;"{% endif %}>
            {{ child.value }}
          </span>
        {% endfor %}
      </{{ heading_size }}>

    {% when 'link' %}
      <a href="{{ item.url }}" title="{{ item.title }}">
        {% for child in item.children %}
          {{ child.value }}
        {% endfor %}
      </a>

    {% when 'list' %}
      {% if item.listType == 'ordered' %}
        <ol>
      {% else %}
        <ul>
      {% endif %}
      
        {% for list_item in item.children %}
          <li>
            {% for child in list_item.children %}
              {{ child.value }}
            {% endfor %}
          </li>
        {% endfor %}
      
      {% if item.listType == 'ordered' %}
        </ol>
      {% else %}
        </ul>
      {% endif %}
  {% endcase %}
{% endfor %}