Last Updated: October 30, 2026
Quick Summary
Managing third-party API integrations during replatforming starts with building a written migration checklist that inventories every integration, maps its dependencies, and scores each on business criticality, migration complexity and vendor risk. Start high-criticality, high-complexity integrations first, then test each one against acceptance criteria before cutover.
- Build the integration checklist in draft form within the first week of planning.
- Score each integration on business criticality, migration complexity and vendor risk using a 1-5 scale.
- Audit and rotate every credential before cutover, storing secrets in a managed vault.
- Test Tier 1 and Tier 2 integrations across six dimensions, including failure-mode and load testing.
- Write the API cutover plan with rollback runbooks before launch week, not during it.
Table of Contents
- Why API Integrations Break During Replatforming
- Build Your Third-Party API Integration Migration Checklist
- Handle Authentication, Credentials and Access Control
- Plan a Phased Migration With Contract Compatibility
- Run Ecommerce API Integration Testing Before Cutover
- Write an API Cutover Plan With Rollback Runbooks
- Choose API Integration Monitoring Tools for Post-Launch
- Book a Free Integration Audit Before Your Next Migration
- Frequently Asked Questions
Why API Integrations Break During Replatforming
Most replatforming projects don't fail at the storefront. They fail in the plumbing behind it.
The reason is structural. If you are moving to Shopify, see how to move to a Shopify store without losing rankings.
Watch out: teams that treat integrations as an afterthought typically discover the breakage in the final week before launch, when there is no time left to rebuild anything properly.
Build Your Third-Party API Integration Migration Checklist
A third-party API integration migration checklist is a written inventory of every system that exchanges data with your store, what it sends, how often, and who owns it. Build it before you touch the new platform.
Most generic integration guides stop at "list your integrations." That list is the easy part. The hard part, and the part that determines whether your cutover succeeds, is scoring each integration, mapping the chains between them, and assigning an owner who can be held to a date.
Inventory Every Integration and Map Its Dependencies
Start with a full sweep: payment providers, ERP, CRM, warehouse management, email and SMS platforms, review tools, subscription billing, tax engines, analytics, and any private apps built in-house.
Then map dependencies between them. A common mistake is inventorying systems in isolation and missing the chains: an order event that triggers a warehouse sync, which triggers a shipping notification, which feeds a CRM record.
Score Each Integration on Criticality, Complexity and Vendor Risk
A flat inventory tells you what exists. A scored inventory tells you what to migrate first, what to migrate last, and what to leave on the old platform indefinitely. Score every integration on three axes, each on a simple 1-5 scale:
- Business criticality, does a failure block revenue, breach a regulatory obligation, or break a customer promise? Payment, tax, and order-routing integrations score highest; internal dashboards score lowest.
- Migration complexity, how much of the integration is tied to the old platform's specific endpoints, authentication model, or data schema? A connector built entirely on legacy webhooks is harder to move than one that talks to a vendor's platform-agnostic REST API.
- Vendor risk, does the vendor already support the target platform, publish a deprecation schedule, and offer a migration path? Or will you be rebuilding the connector yourself?
Plot the scores. High-criticality, high-complexity, high-vendor-risk integrations are your critical path and need to be started first, not last. Low-criticality, low-complexity integrations can move in a later wave or be retired entirely.
Assign an Owner and a Vendor Contact to Every Row
An integration without a named owner is an integration that will be discovered broken in launch week. For each row in the checklist, record:
- The internal owner accountable for the integration working on the new platform.
- The vendor's technical support contact and escalation path, not the sales contact.
- The vendor's published SLA and support hours, and whether those hours cover your cutover window.
This is also where you surface contract issues early. Check whether your vendor agreement covers the target platform, whether a plan tier change is required, and whether the vendor charges for a re-implementation. Discovering a contract gap two weeks before launch is a schedule problem you cannot compress.
Rank by Business Criticality to Define Day-One Scope
The output of this exercise is a tiered list. Tier 1 integrations must work on day one with zero tolerance for silent failure. Tier 2 can tolerate a short degraded window with manual workarounds. Tier 3 can wait a week or more. Write the tier definitions down and get sign-off from the business owner before migration work begins, because the tier list is what you will point to when someone asks why their integration is not in the first wave.
Score every integration on three axes, each on a simple 1-5 scale, to decide what moves first.
| Scoring axis | What it measures | Example |
|---|---|---|
| Business criticality | Does failure block revenue, breach regulation or break a promise? | Payment, tax and order routing score highest |
| Migration complexity | How much is tied to old platform endpoints, auth or schema? | Legacy webhook connectors are harder to move |
| Vendor risk | Does the vendor support the target platform and publish a migration path? | Otherwise you rebuild the connector yourself |
Handle Authentication, Credentials and Access Control
Authentication is the most common silent failure in a migration. Every integration authenticates somehow, whether through API keys, OAuth tokens, or signed requests, and those credentials are usually tied to the old platform's app registration.
Audit every credential before cutover. For custom integrations and private apps, see custom Shopify functionality when apps stop being enough. The European Commission's GDPR guidance sets out those obligations clearly.
Plan a Phased Migration With Contract Compatibility
Big-bang cutovers are where migrations go wrong. A phased approach moves integrations in waves, grouped by criticality and dependency, so each wave can be validated before the next begins.
Check contract compatibility before each wave. Vendors publish API versions and deprecation schedules, and an integration built against an older version may not behave the same on the current one. For teams planning a high-volume move, our guide on enterprise ecommerce cutover strategy walks through sequencing in more detail.
Run Ecommerce API Integration Testing Before Cutover
Ecommerce API integration testing is the practice of validating every data flow against the new platform before live traffic touches it. Rigorous validation of these transactional flows ensures that the system remains stable when you migrate customer data to the new architecture.
Generic advice stops there.
Build a Test Matrix Across Six Dimensions
For every Tier 1 and Tier 2 integration, run tests across six dimensions and record pass/fail per dimension. A single "it works" tick is not enough.
- Contract testing, does the request and response payload match the vendor's current API version? Validate field names, types, required fields, and enum values against the vendor's published schema, not against what the old platform happened to send.
- End-to-end flow testing, does a real business event (order placed, refund issued, stock adjusted) propagate correctly from the new platform through to the downstream system and back?
- Security testing, are credentials scoped to least privilege, are tokens short-lived, and does the integration reject malformed or unauthorized requests? The OWASP API Security Top 10 is a useful checklist for the security side of this testing.
Use a Deliberate Environment and Data Strategy
Staging environments rarely mirror production exactly, and that gap is where migration testing fails. Decide explicitly what "realistic data" means for each integration:
- Use a production-derived dataset with personal data masked or synthetic, so volume and edge cases are representative without creating a data protection problem.
- Confirm the vendor's sandbox behaves like production for the endpoints you depend on, some vendor sandboxes skip rate limiting, tax calculation, or webhook delivery, which hides exactly the failures you need to catch.
- Test against the specific API version you will run in production, not the vendor's default or latest.
Define Acceptance Criteria Before You Test
Write the pass condition for each integration before testing begins, and get the business owner to agree it. Examples: "Order count in ERP matches platform order count within 0.1% after a 24-hour test run," or "Refund issued on the new platform appears in the payment provider and CRM within five minutes." Acceptance criteria turn testing from an opinion into a gate, and they give you the evidence you need to decide whether an integration is ready for its cutover wave.
Reconcile Data Before and After Each Wave
Data reconciliation is the step teams skip and then regret. Before each cutover wave, capture baseline counts and totals from the old platform. After the wave, compare the same figures on the new platform and in every downstream system. Investigate every variance, even small ones, a persistent 0.5% order mismatch is usually a dropped webhook or a timezone boundary, and it will grow once live traffic arrives.
Write an API Cutover Plan With Rollback Runbooks
An API cutover plan is a sequenced, timed document that states exactly which integrations switch over, in what order, who executes each step, and how to reverse it. Write it before launch week, not during it.
Rollback runbooks matter more than most teams admit. Our guide on migration downtime risks covers cutover and rollback in more depth. For each critical integration, document how to revert to the previous state, how long the revert takes, and what data reconciliation is needed afterward.
Choose API Integration Monitoring Tools for Post-Launch
Launch is not the finish line. Integrations degrade quietly: a vendor changes a response format, a token expires, a rate limit tightens, and orders stop syncing without anyone noticing until customers complain.
Look for tools that alert on failure thresholds, log full request and response payloads for troubleshooting, and give you a single dashboard across all integrations. The Shopify API rate limits documentation is worth bookmarking, since throttling behaviour is one of the most frequent post-launch surprises.
Book a Free Integration Audit Before Your Next Migration
The pattern across every migration we handle is the same: the integrations that were documented and tested early caused no trouble, and the ones nobody remembered caused all of it. Before your next replatforming project, get an independent read on what you're actually running. Conversion Design offers a free audit, so you can see where your integration risk sits before it becomes a launch-week emergency.
Frequently Asked Questions
How do you manage third-party API integrations during a replatform?
Start with a full inventory of every API integration, its owner, its data flows and its rate limits. Map dependencies between systems, then define which integrations move in phase one and which can run in parallel on the old platform. Handle credentials through a secrets manager, test each integration against a staging environment, and cut over in a fixed order with a rollback runbook ready. Monitoring after launch confirms data synchronization is actually working.
What should an API cutover plan include before switching integrations over?
An API cutover plan should list the switch-over order, who owns each step, the exact time window, and the rollback trigger for every integration. Include a freeze on unrelated changes, a contact list for each vendor, and a verification step that confirms data exchange after each switch. Keep the old integration credentials active until the new ones have passed a full business day of monitoring, so you can revert without rebuilding anything.
How can you prevent data loss when migrating API integrations?
Run the old and new integrations in parallel for a defined period, compare records on both sides, and only retire the legacy connection once the counts match. Log every request and response during the transition so any gap can be replayed. For order, customer and inventory data, set up a reconciliation check that runs daily and flags mismatches early, rather than discovering them weeks after cutover.
How do you monitor integrations after an ecommerce replatform?
Track error rates, latency and failed requests per integration, and alert on thresholds rather than waiting for a merchant to report a missing order. Use retry logic with exponential backoff for transient failures, and keep logs long enough to trace an issue back to its source. Review the dashboard weekly for the first month, then monthly, and confirm that each integration still meets its service-level agreement.
Replatforming exposes every weak point in your integration layer, and the brands that come through it cleanly are the ones that planned for breakage instead of hoping to avoid it. Conversion Design handles migrations with zero-downtime cutovers, a senior team on every project, and fixed scope and pricing, so integration work doesn't quietly expand your budget. Get started with Conversion Design and move to your new platform without losing rankings, orders or revenue.
