When building fintech applications, letting the client dictate when to fetch third-party banking data will eventually destroy your API rate limits and skyrocket your cloud bill.

Today, I tore down my reactive data-fetching logic and replaced it with a resilient, event-driven webhook architecture using AWS Lambda, Amazon SQS, and DynamoDB. Here is how I solved the core architectural bottlenecks in my Serverless Financial Agent.

Fixing the Stale Dashboard & Identity Resolution

My React dashboard was showing stale data, while the daily automated emails had real-time numbers. The root cause? An identity partition mismatch. The background worker was using a default ID, while the frontend sometimes resolved to an email address instead of the strict Cognito sub ID. I unified the identity resolution algorithm so both endpoints read and write to the exact same DynamoDB partition.

Event-Driven Sync Pipeline

I deprecated the dangerous user-triggered "Force Sync" pattern.…