Legacy ASP.NET Web Forms Developer Needed: Klaviyo API Integration (Profiles + Events, backend only)

Overview We need an experienced ASP.NET (classic Web Forms) developer to implement a custom Klaviyo API integration for our ecommerce site. This is a backend, API-only implementation. We are not using Klaviyo plugins, and this is not Shopify/WooCommerce/BigCommerce. Our backend is a legacy .NET ecommerce codebase (ASPDotNetStorefront v1). A detailed integration specification is provided that defines exact event names, payload properties, and requirements. Your job is to implement what’s in the spec, not redesign the data model. Scope (what you will build) Implement server-side calls to Klaviyo: Profiles API (server-side only) for customer profile create/update and consent fields Events API (server-side preferred) for ecommerce lifecycle events Client Events API (optional fallback) only if needed for specific onsite tracking Required events (must match names exactly) HVS – Site Visit (fire once per session, debounced) HVS – Viewed Product HVS – Added to Cart HVS – Started Checkout HVS – Placed Order (server-side only, after successful payment) HVS – Subscription Started (server-side only) Optional events (quote separately, if feasible) HVS – Fulfilled Order HVS – Cancelled Order HVS – Refunded Order Key requirements Event payloads must be normalized and include the properties defined in the spec (including line_items arrays where required). Consent handling is required: email_marketing_consent and sms_marketing_consent must include boolean value, timestamp, and source (checkout, account creation, popup, etc.). All timestamps must be ISO-8601 UTC. Klaviyo private API keys must remain server-side only. Implement retry logic for transient failures (for example 5xx responses) and basic error logging. This role is strictly implementation. It does not include Klaviyo flows, email/SMS creative, analytics strategy, or general frontend tracking beyond what the spec explicitly requires. Deliverables Working implementation in staging, then production. Verification evidence (screenshots or short recording) showing each required event arriving in Klaviyo with correct properties. Short handoff note: configuration needed (API keys, site ID), where hooks were added, and how to test each event. Time and budget We believe this is a short project for the right senior dev. Please review the spec and propose your estimate. We prefer a fixed-price milestone approach: Milestone 1: required events + profiles/consent + basic retries/logging Milestone 2 (optional): fulfilled/cancel/refund events and any hardening To apply (required, we will ignore proposals that don’t answer): Have you worked in classic ASP.NET Web Forms and legacy ecommerce codebases? Briefly describe similar work. Where would you hook each event in a typical Web Forms ecommerce flow (product view, cart update, checkout entry, payment success, subscription creation)? How will you handle identity when a user is anonymous at first and provides email later (checkout/account)? How will you implement retries/logging while minimizing duplicate events? What is your estimated time to complete Milestone 1, and when can you start? Apply tot his job Apply To this Job