Studio 4.0.0 Adding Line Items do not show in cart/at checkout

Store Design

Topic summary

A user upgraded to Shopify’s Studio Theme 4.0.0 and encountered an issue where custom line items added through a product template no longer appear in the cart or at checkout.

Steps taken:

  • Created a custom product template (“car-seat-ponchos”)
  • Added custom line item code to main-product.liquid using Shopify’s Line Item Property generator
  • The custom options display correctly on the product page but fail to pass through to cart/checkout

Troubleshooting in progress:

  • Another user (Tristram) identified that the custom select elements are missing required attributes
  • Specifically, each select needs: a unique id, unique name, and a form attribute matching the product form
  • The user should reference the quantity input field to find the correct form attribute value to use

Current status: The issue remains unresolved. The user has attempted updates but continues experiencing the same problem with line items not appearing at checkout.

Summarized with AI on November 25. AI used: claude-sonnet-4-5-20250929.
1

I updated to Theme: Studio 4.0.0 and my Custom Product Templates using line items is no longer showing in the cart and at checkout.

I have done the following:

  1. Clicked Online Store → Theme → Customize (after duplicating so I don’t mess up the live site)
    1. Top of the Screen → Clicked Products → Create Template "car-seat-ponchos’
    2. Went back into my product list and assigned product to this template
  2. Online Store → Theme → Edit Code

Searched the “main-product.liquid” for the following code

{%- assign product_form_installment_id = 'product-form-installment-' | append: section.id -%}
{%- form 'product', product, id: product_form_installment_id, class: 'installment caption-large' -%}​

Added the following code just below it (created using Line Item Property )


{% if product.template_suffix == 'car-seat-ponchos' %}

    

    

    

    

{% endif %}

The options show up on the correct product when I go to my website (seen here: Product Page on Website). However, the options down not show at checkout (nor on my end when purchased).

What am I doing wrong? How can I get this working?

Do I need to edit the following product (I did not create this - it showed up when I added the custom product template).

product.car-seat-ponchos.json
2

the second option needs a unique id and unique name and you need the form as well, but I’m not exactly sure what your form code looks like but you could try:


you should be able to confirm what the form="" should look like down on the quantity input.

But both selects needs the form, and the second one needs a unique id="" an name=""
3

Like this? I updated the name and label. But I get the same problem.
4

I updated it to this and it is still not working:

{% if product.template_suffix == 'car-seat-ponchos' %}

    

    

    

    

{% endif %}
5

You’re missing the form attribute. After “select” you will need form=“somethng here”. My best guess is below, but the quantity input will have the same attribute that you’ll need.