A shopper may choose products, enter a postcode to check delivery, and return to an empty cart. The owner sees abandoned sessions; the buyer experiences a broken promise. A page redesign cannot be specified responsibly until someone reproduces the sequence and finds the state change. The fault could involve a delivery app, theme script, checkout redirect, session cookie, or an incompatible combination.
Treat the complaint as a reproducible technical hypothesis. Do not assume that every postcode checker behaves the same way, or that the checker itself is at fault simply because the cart changes afterward.
Reproduce it like a customer
Write down the exact path before touching code: product URL, variant, quantity, postcode, delivery option, device, browser, login state, and whether the customer accepted cookies. Record a short screen capture with test data. Repeat with a different postcode and a clean browser session. Does the cart reset immediately after the check, only after a page reload, or only when the shopper proceeds to checkout?
Check the cart line items before and after each transition. If the postcode checker opens a new domain or embedded app, note where the session changes. If it updates delivery eligibility but the item itself remains, avoid describing the issue as cart loss. The precise symptom directs the right developer or app vendor.
Decide where eligibility belongs
Some stores must check serviceability before they can quote a delivery date. If so, show that check early enough to prevent a late surprise, but do not ask for unnecessary location data before the shopper understands the product. If a postcode cannot be served, explain what happens next: another delivery method, collection, or no available order route. Do not promise nationwide delivery on the product page while a later checker excludes many addresses.
If the checker must hand off to another service, define a testable requirement: variant, quantity, and cart total remain intact after an eligible postcode is entered; an ineligible postcode leaves the cart visible and gives an understandable message. This is more useful in a technical brief than “improve checkout UX.”
Verify the repair across the real paths
Test guest and returning customers, mobile and desktop, eligible and ineligible postcodes, multiple items, and browser back navigation. Make a low-value test order where appropriate. Record the result after every app or theme update that touches delivery. If customers reported the issue, keep their contact details out of the bug report and use a test order instead.
ARCHV can help scope the customer path and acceptance test. The postcode app, cart state, delivery rules, and checkout implementation are custom commerce work requiring platform access and a separate quote. Request a website estimate with the affected URLs, reproducible steps, and your current delivery rules.
Further reading: Shopify's shipping-rate setup explains platform shipping configuration. It does not diagnose a specific app conflict.
If the team cannot reproduce a reported failure, capture the affected session time and anonymized order context, then ask the platform or app vendor which logs are available. Avoid asking the customer to repeat a failed checkout indefinitely. A clear temporary service route can protect the sale while the technical cause is investigated.