Define a canonical data model and designate a single system of record for each field (e.g., HRIS owns employee name and department; payroll system owns pay rate and bank details) before building any reconciliation logic.
Subscribe to webhook events from both the payroll provider and HRIS — map event types (hire, termination, pay run completed, salary change) to the fields they affect in your canonical model.
On receiving a webhook, validate the event signature using the provider's documented HMAC or signature scheme, then enqueue the event for idempotent processing (use the event ID to deduplicate retries).
Compare the incoming event data against your system of record: if the event originates from a non-authoritative system for that field, log a conflict rather than overwriting the authoritative source.
Implement a reconciliation job that periodically full-syncs both systems and flags discrepancies — webhook delivery is not guaranteed, so treat event-driven sync as best-effort and scheduled reconciliation as the source of truth backstop.
Known gotchas
Webhooks can arrive out of order or be delivered more than once — always process events idempotently using the event ID and compare effective dates before applying updates, not just arrival order.
Payroll providers often emit events on a processing cadence (e.g., after a pay run closes) rather than in real time when changes are made — data visible via webhook may reflect a batch-processed state, not an instantaneous change.
Silent sync failures are the most dangerous failure mode: build alerting on webhook delivery failures, missed expected events (e.g., no pay run event on a known payroll date), and divergence detected during reconciliation sweeps.
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