How to create a personalised box in Shopify for free?

              
{% for t in product.tags %}
     {% if t contains 'Customized' %}    
<p class="line-item-property__field">
        <label for="personalise">Personalised</label>
        <input id="personalise" type="text" name="properties[personalise]">
      </p>  
{% endif %}
{% endfor %}

Add a tag ‘Customized’ to your product.

And then the add the above code in your product-template liquid file above the qty section to display the personalised name box.