Add custom text field to Shopify contact form with HTML
<!--
Add the below code to your page.contact.liquid file
Note: dont forget to repalce the "dummy text" (Birthday) with your own value!
-->
<label for="ContactFormBirthday">Birthday</label>
<input
type="text"
id="ContactFormBirthday"
name="contact[Birthday]"
placeholder="Birthday"
/>
<!--
Bonus: This is where you will find all the info that you need (link below):
https://shopify.dev/tutorials/customize-theme-add-fields-to-your-contact-form#customize-your-form-fields
-->
<!-- Happy coding, my homies <3 -->