Need to add a customAttributes to order.lineItems 'Start' in the POS.

[ConundrumHouse]

We use an Online app BookThatApp for our webstore that handles rentals and tracks when a booking starts with a custom attribute of Start and the date the rental started.
When the POS creates such a rental, the online app doesn't trigger (as the custom function that handles adding the custom field is part of the online checkout cart) but it seems to me I ought to be able to have either a flow that adds the custom field if orders with rentals are created, or have some POS App API function that does it. 

For Flow, there seems to be no way to alter an order line item, but I can see it if it is there - eg in email to staff I can:

{% for li in order.lineItems %}
{% for ca in li.customAttributes %}
{{ ca.key }}
{{ ca.value }}
{% endfor %}{% endfor %}

Prints 

    Start
    07/21/2024

I hope I am missing something. ( so for rental orders created online, this data is present, but for orders created in the POS for the same rental product, it is absent.)

And I got rather tangled up in the weeds of how to create a POS App API that does this given the nature of Shopify reference documentation.

so how to proceed?

Thanks for looking.

|\\/|ark

[AchieveApplabs]

Hi Mark,

There is a way to edit order line item in POS. You create what’s called a POS UI Extension. This adds a smart tile to your POS that exposes the cartAPI: https://shopify.dev/docs/api/pos-ui-extensions/2024-04/apis/cart-api#cartapi-propertydetail-addlinei...