How can I fix the issue when the cart becomes empty after clicking the checkout button on the cart page?

This is a known issue with some Themes. It occurs if the cart page has non-standard line item quantity inputs in your theme. The app can not properly get the line item quantities, so the line item is removed from the cart.

The app relies on the fact that all the quantity inputs have id attribute with line item variant id inside. Usually the id attribute looks like "updates_742384782", where 742384782 is Shopify variant ID.

There are 2 possible cases:

     1. line item quantity input in your theme doesn't have the id attribute at all or this attribute doesn't contain variant ID value. 

         Example: {‌{id="updates_{‌{ }‌}"}‌}.

     2. line item quantity input in your theme contains variant ID inside the id attribute, but it has another prefix (not "updates_").

In the case (1) you need to modify/add the id attribute to make it look like " id="updates_{‌{ }‌}" ". Just use corresponding liquid variable in the cart.liquid

                                                                                      (click to enlarge)

In the case (2) you need to 

  1. Open Themes section on the admin panel of your web store (Online Store → Themes);

  2. Find Theme from the list which will be used with our installed app.

  3. Click Actions  Edit Code.

  4. Add the following code to the beginning of the cart.liquid file under Templates section:

<script>SPOCustom = {}; SPOCustom.cartQuantitySelector = "[id^='your_prefix_here:id']";</script>