POS Cart Transform lineUpdate completes successfully, but line item price unchanged and "Couldn't load checkout" error

[derrick]

Hi team,

We have reports of this intermittent behavior from a Shopify Plus merchant using our app: Price Embedded Barcode Scanner - Scan price-embedded barcodes into your POS cart! | Shopify App Store

Our app adds a line item and then applies line item properties, and we have a Cart Transform function installed to then perform a lineUpdate operation based on these properties. In this merchant’s case, they intermittently experience an issue where the line item’s price does not adjust in the POS cart, and then immediately afterwards they run into a "Couldn't load checkout" error.

Video of the issue here: https://drive.google.com/file/d/1LjUJ6A7bOIGhnmv3UAjmZ9hp_BJyQ49Z/view?usp=sharing

We believe we have matched the Shopify Functions invocation ID to the timestamp of their video, it’s either of the below. From the logs all of the line item properties are being applied correctly and all functions for their shop are returning OK.

1c390987-a54a-451b-bb1e-4cd833db1e04    Sep 16, 2026, 2:45:36 PM EDT (18:45:36 UTC)
db14a891-a7b3-42ef-9989-63fa9fc53326    Sep 16, 2026, 2:45:38 PM EDT (18:45:38 UTC)

Merchant also says they have no other POS apps installed in their store and we verified this on our end.

Based on the timestamp and logs, is there anything you can see from your end as to what’s causing the errors?

Thanks,

[derrick]

We spoke to the merchant and they shared the issue isn’t intermittent, it’s happening 100% of the time to specific products. Upon digging into their Shopify account, we determined that they didn’t have their “All Regions” catalog set for these specific products.

vs.

Shopify team, is it possible to get more specific error handling than “Couldn’t load checkout?” Or to return some kind of error in the POS cart itself, if a product isn’t part of a required regional catalog?

As an aside, this is the second time now where something related to catalogs has broken functionality with our POS UI Extension: Can't add API-created product to POS cart affecting specific merchants - #3 by derrick

[Paige-Shopify]

Thanks for sharing your findings, @Derrick. The “Couldn’t load checkout” error can occur when a POS UI extension adds a product that isn’t available in the current region.

I’ve submitted a request for a more useful error message in these cases so the underlying catalog configuration issue is easier to identify.