Custom Shopify apps, checkout & paymentsClient work
Attaching a non-native payment provider to Shopify: a documented feasibility spike, a legal-risk memo for counsel, then the build.
Sounds familiar?
How I solve it
I build this in stages, starting with a documented feasibility spike. Every attachment point Shopify checkout exposes is tested as a numbered experiment, with a written verdict, and a blockers register of what does not work. Then I write a legal-risk memo in plain language your counsel can act on — this is technical implementation, not legal advice. Only if a working path exists do I build it: a custom-distribution Shopify app with checkout UI extensions for the pay, retry and confirm flow, webhook signature verification, and a single correlation rule. The rule is strict: only the provider’s paid status marks an order paid, never a browser return, and every order marking is read back from the API.
The process
6 steps. Scope and a fixed price are agreed before the first one.
as a numbered experiment with a result schema and a verdict.
— what fails, and why.
for your counsel, citing Shopify's terms.
Only a working path goes forward to the build.
checkout UI extensions for pay, retry and confirm.
signed webhooks, one idempotent correlation rule, read-back on every marking, then a rollback image and health checks.
Handover
Built with
Proof
Client work Done for real clients. Client details are anonymised.
Before → after
Shopify offered no native gateway for the provider, so the work began as a spike across every attachment point — experiments A to U, each with a verdict. One working path shipped: the first complete payment was recorded on 2026-09-09, the backend has been live since 2026-09-15, and the correlation module passes 96 of 96 tests. Client acceptance is pending.
EU Shopify Plus merchant
96/96
a non-native card and crypto provider attached to checkout: four checkout UI extensions, signed webhooks, one idempotent correlation rule — only the provider's paid status marks an order paid, never a browser return. 96 of 96 tests pass; client acceptance is pending.
goes above and beyond when completing tasks.
What you can look at
A redrawn decision tree from the spike — attachment point → verdict → blocker — on synthetic data, plus the correlation rule written out: “only the provider’s paid status marks an order paid; never a browser return.” Figures below are from the engagement’s evidence protocol.
Client details anonymised. Figures come from the engagement's evidence protocol and deploy records, 2026. This covers technical implementation on Shopify, not legal advice.
Price and timeline
The spike and the build are separate Custom Engineering Projects, each from USD 1,500, scoped and quoted in writing. If all you need is the go/no-go answer on one attachment point, a Technical Working Session at USD 195 can give it. Discussing the task is free.
QuoteFixed before work starts
A note from Daniilbefore you decide
You need this only if a standard provider cannot serve you. Before any build, your counsel signs off on Shopify-terms risk first — I write the memo, they make the call. And if the only attachment point left is one that breaks at the return step, the honest answer is no, and I will say so before taking the build.
— Daniil
Questions
That is a legal question, not a technical one. I document the risk in a memo your counsel can read; the decision is theirs. This is technical implementation, not legal advice.
If an app supports your provider, use it. This is for providers Shopify does not support natively, where there is no plugin to install.
Only the provider's paid status marks it paid. A browser return URL is never trusted, and every order marking is read back from the API to confirm.
Then the answer is no, and you have a written record of what was tested and why it failed. That is the point of doing the spike before the build.
A plain-language write-up, with citations to Shopify's terms, of where the approach sits and what to ask your counsel. I am not a lawyer and do not give legal advice.
The first answer is free, within one working day. Or write directly: next@taskfordaniel.com
