Senior Engineer for Server-Side Tracking Pipeline Data Integrity & Reconciliation

We are seeking an experienced engineer to take ownership of our server-side tracking pipeline, focusing on resolving critical data-integrity issues and ensuring accurate event delivery across all destinations. Our current pipeline is live in production, built on a serverless Google Cloud Run endpoint that ingests webhooks, utilizes Firestore for idempotency and signature validation, and fans out data to GA4 Measurement Protocol, Meta Conversions API, TikTok Events API, and an affiliate platform. This is not a greenfield project but a precision job on an existing live system where data reconciliation is paramount.

Known issues that require immediate attention:
- Purchase value discrepancies in GA4: The pipeline currently forwards the plan's list price instead of the actual amount charged, leading to revenue reconciliation issues with Stripe due to discount coupons.
- Missing refund events in GA4: Refund events are not reaching GA4, and the root cause needs to be identified and resolved.
- Lack of join key for purchases and refunds: Purchase and refund events originate from different upstream sources without a common field to link them. Our proposed solution involves keying on the Stripe customer ID with a Firestore lookup, but we are open to alternative, more robust designs.
- High endpoint latency: The current endpoint latency is approximately 18 seconds, which risks duplicate deliveries from webhook providers due to retry mechanisms.

Project success will be validated against the live production environment, not solely through documentation. The engagement will conclude upon demonstrating the following:
- GA4 accurately displays purchase and refund events under the same transaction_id, with values that precisely reconcile against Stripe transactions.
- Meta Events Manager and TikTok Events Manager successfully show the receipt of all relevant events.
- The corresponding Cloud Run logs confirm correct event processing.

Testing will involve real transactions with natural webhook firing, using a provided test coupon and address. Hand-posting synthetic payloads will not be accepted as proof of resolution. An NDA will be required before access to the system.