Checkout customization migration to Shopify

During discovery, build an explicit inventory of every customization in the source-platform checkout: custom fields with their data destinations, business rules with their trigger conditions, discount logic with edge cases, payment routing rules, post-purchase flows. Most of this lives in source-platform configuration that is invisible until inventoried.

The inventory exercise almost always surfaces customizations the operations team had forgotten about — fields added years ago for a one-off integration, rules that handle specific customer segments. Surface these in discovery; the cost of forgetting them is post-launch incidents during specific scenarios that nobody catches until customers complain.

For each inventoried customization, decide whether it can be reproduced via Shopify Plus checkout extensibility (UI extensions, Shopify Functions for discounts and shipping, custom validation), reproduced via apps from the Shopify App Store, or must be retired as part of the migration. The decision belongs in discovery, before build phase.

Checkout extensibility covers more than it did even two years ago, but not everything. Custom field collection, custom validation, custom shipping methods, and discount logic are well-supported. Truly arbitrary payment routing, complex multi-step custom flows, and inline custom UI beyond extension points are still hard. Be honest about what extensibility supports; do not over-promise based on what extensibility might support in the future.

The migration is an opportunity to simplify the checkout. Many source-platform customizations were responses to constraints that no longer exist on Shopify, or solutions to problems that have better-supported alternatives now. Identify the customizations whose retirement actually improves the checkout experience; brands often discover that simpler checkouts produce better conversion rates.

Communicate the retirement decisions to internal stakeholders early. Customer service, finance, and operations teams sometimes depend on specific checkout fields for downstream workflows. Retiring those fields without updating the downstream workflows produces operational friction that exceeds the simplification benefit.

Before cutover, run end-to-end checkout testing for every customer scenario the brand serves: B2B, B2C, gift orders, international, subscription, wholesale, exempt customer, high-value, low-value, multi-discount stack. Each scenario can fail differently; testing each one specifically catches the issues that single-scenario testing misses.

The testing pass is operationally simple but easy to compress when timeline pressure builds. Brands that compress checkout testing consistently surface customer-facing checkout incidents post-launch; brands that protect the testing window catch the issues in staging where they belong.