Snippet of abandoned checkout email notification to load a discount - https://www.shopify.com/partners/blog/shopify-email-notifications

email-notification-discount-code.liquid

<td class="button__cell">
  <a href="{% if url contains '?' %}
    {{ url | append: '&discount=WelcomeBack' }}
  {% else %}
    {{ url | append: '?&discount=WelcomeBack' }}
  {% endif %}" class="button__text">Complete your purchase</a></td>
  </tr>
  </table>
    {% if shop.url %}
      <table class="link secondary-action-cell">
  <tr>
     <td class="link__cell"><a href="{% if url contains '?' %}
       {{ url | append: '&discount=WelcomeBack' }}
     {% else %}
       {{ url | append: '?&discount=WelcomeBack' }}
     { % endif %}" class="link__text"><span class='or'>or</span> Visit our store</a>
</td>