Sync Shopify and eBay

In short

Syncing Shopify and eBay means holding one master catalogue and pushing stock changes to both channels the moment anything sells. Without it, the same unit stays listed on the second channel until someone updates it manually, which is how oversells and cancelled orders happen. SBD has run this pattern across three channels with zero mismatches.

The workflows

What runs between Shopify and eBay.

Each line is one automated workflow. An event in one tool, the checks and mapping in between, the action in the other, and the person who hears about it.

1. Single-unit and low-stock inventory where oversell is unacceptable

   When

   Sale on either channel

   Automation

   • Verify and validate
   • Map and normalise
   • Upsert by key

   Then

   Decrement master stock and push the new level to every other channel immediately

   And

   • Audit log entry
   • Alert if it fails or goes quiet
   • Review queue if unsure

2. Launching products to multiple channels without duplicate data entry

   When

   New product added to the master catalogue

   Automation

   • Verify and validate
   • Map and normalise
   • Upsert by key

   Then

   Create the listing on both channels with channel-correct fields and taxonomy

   And

   • Audit log entry
   • Alert if it fails or goes quiet
   • Review queue if unsure

3. Channel-specific pricing from one catalogue

   When

   Price or content updated centrally

   Automation

   • Verify and validate
   • Map and normalise
   • Upsert by key

   Then

   Propagate to both channels, respecting per-channel pricing rules

   And

   • Audit log entry
   • Alert if it fails or goes quiet
   • Review queue if unsure

4. Adding a third marketplace without adding manual work

   When

   Stock reaches zero

   Automation

   • Verify and validate
   • Map and normalise
   • Upsert by key

   Then

   End or hide the listing on every channel rather than leaving it orderable

   And

   • Audit log entry
   • Alert if it fails or goes quiet
   • Review queue if unsure

Every record passes through the same stages

1. 1Receive

   Webhook or polling from the source tool, with a signed payload and a replay log.

2. 2Validate

   Required fields present, types right, record key found. Anything else goes to the review queue.

3. 3Map

   Fields translated to the destination schema. Enumerations, currencies and dates normalised.

4. 4Upsert

   Written against the record key, so a retry updates rather than duplicates.

5. 5Confirm

   Outcome logged. Alert if the count goes quiet. Reconciliation run nightly.

Read this first

Why the obvious route breaks.

A one-step Zap connects Shopify and eBay in an afternoon. This is what goes wrong once real volume and real edge cases arrive.

• Neither platform will be the master

  Point-to-point sync forces you to pick a winner, and both platforms accept orders independently. The moment two sales land close together, whichever direction you chose loses one of them. A separate master catalogue is the only arrangement that holds.

• Listing structures do not map cleanly

  eBay item specifics, category taxonomy and variation structure do not correspond one-to-one with Shopify variants. A naive field-to-field copy produces listings that are either rejected or badly formed.

• Polling is too slow for stock

  Off-the-shelf connectors often poll every 15-30 minutes. For single-unit or low-stock inventory that window is exactly when you oversell. Stock decrements have to be event-driven.

• eBay rate limits will bite at scale

  The eBay API caps calls per day per application. A sync that updates every listing on every change hits the ceiling and starts silently failing, so updates need batching and prioritisation by what changed.

What it costs today

The gap, as the team feels it and as the engineer sees it.

What we wire up

The data flows.

1. 01
   When

   Sale on either channel

   Then

   Decrement master stock and push the new level to every other channel immediately

2. 02
   When

   New product added to the master catalogue

   Then

   Create the listing on both channels with channel-correct fields and taxonomy

3. 03
   When

   Price or content updated centrally

   Then

   Propagate to both channels, respecting per-channel pricing rules

4. 04
   When

   Stock reaches zero

   Then

   End or hide the listing on every channel rather than leaving it orderable

Data map

What becomes what, and what it is keyed on.

Field-level mapping is agreed in the blueprint and written into the runbook. Two-way rows carry loop protection so a write from the sync never re-triggers the sync.

In every build

What you get with the sync, whichever pair.

Security and your data

Where the data goes, and who holds the keys.

Accounts

Every platform account is created in your name. We work through managed access you can revoke.

Credentials

Stored encrypted in the orchestration layer. Scoped per connection. Rotated on handover.

Data in transit

TLS everywhere. Webhooks verified by signature before anything is processed.

Data at rest

Only what the sync needs. No copies of your customer data on our machines.

AI steps

Where an integration uses a model, it is through a business API that does not train on your data.

Retention

Run logs kept 90 days by default, adjustable. Payloads redacted of card and ID numbers.

Agreements

DPA and NDA on request. Regional rules covered in our privacy policy.

Keys and sensitive data

How API keys, tokens and personal data are handled.

• Keys live in a vault, never in code

  API keys and tokens are stored in the orchestration layer's encrypted credential store or the platform's secret manager. None are written into workflows, repos, spreadsheets or chat.

• One credential per connection

  Each integration gets its own key, scoped to the objects and actions it needs. A lead sync cannot read invoices. Revoking one key stops one thing.

• Service accounts, not personal logins

  Connections use a dedicated service user in your account, so nothing breaks when a person leaves and nothing runs under someone's name.

• Two-factor on every account

  Every platform account we set up has two-factor authentication on, with recovery codes handed to you, not kept by us.

• Rotation on handover and on request

  Keys are rotated when the build is handed over, when anyone with access leaves, and at any time you ask.

• Secrets never reach the logs

  Audit logs redact tokens, card numbers, government IDs and anything you flag as sensitive before a line is written.

• Webhooks verified before processing

  Inbound calls are checked against the sending tool's signature. Unsigned or stale payloads are dropped and counted.

• Access you can see and revoke

  Our access is through managed roles in your accounts. You can list it, limit it, and remove it in one click without touching the build.

Engineering decisions

Decided before the first workflow is written.

• Rate limits and backoff

  Every API has a ceiling. Calls are batched, queued and retried with increasing delays so a busy hour does not become a failed one.

• Backfill and pagination

  The first run has to load history, not just new events. Backfills page through the source in order, resume after interruption, and never double-write.

• Out-of-order and duplicate events

  Webhooks arrive twice and out of sequence. Each event carries a version or timestamp, and older versions never overwrite newer state.

• Schema changes

  A renamed field or a new dropdown value is the most common silent failure. Payloads are validated against a contract, and a mismatch stops the run and raises a flag.

• Time zones, currencies, units

  Dates are stored in UTC and shown local. Money carries its currency. Quantities carry their unit. Conversions happen once, in the map step.

• Sandbox first

  Builds run against sandbox or test accounts with seeded data before they touch production. Go-live is a switch, not a rewrite.

• Versioned and reversible

  Workflows and code are version-controlled. A release can be rolled back in minutes without losing the records processed since.

• API deprecations watched

  Tools retire API versions on a schedule. We track the dates for every connection in the runbook and upgrade before the cut-off.

• Cost per run known

  Each workflow has a cost per execution, including any model calls, logged alongside the run. You see the bill before it arrives.

• Metrics, not just errors

  Runs per hour, records in and out, exception rate and latency are charted. Trends show a problem before an alert does.

Proof

Where we have done this.

• Customer story

  Sales channel inventory sync

  Exactly this build for a D2C watch reseller across Shopify, eBay and Chrono24, zero inventory mismatches and twice the listing speed.

  Read the story →

Questions

What people ask about this pair.

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