Server-side GTM + Meta CAPI specialist — fix WooCommerce/FunnelKit upsell tracking & deduplication

To je polje za opis. Prilepi tole (že prilagojeno za copy-paste, isti opis kot prej): We run a WooCommerce + FunnelKit DTC store (Italian market) with a hybrid Meta tracking setup: a web GTM container feeding a Stape server-side container, sending events to Meta's Conversions API. Most of the setup already works and has been diagnosed. We need an experienced server-side tracking specialist to finish and validate the remaining issues — this is not a "figure out why nothing works" job, it's well-defined. CONFIRMED WORKING: fbclid → _fbc capture via a custom GTM init tag, verified reaching Meta with Click ID Server-side Purchase via Stape CAPI, arriving with Email, Phone, Click ID, IP Event Match Quality ~8/10 ISSUES TO FIX: One-click upsell events are not tracked. Our gtm-tracking.php only covers view_item, add_to_cart, checkout and the main purchase — there is no hook into FunnelKit's upsell lifecycle (wfocu_offer_accepted_and_processed). Upsell revenue is missing from reported values. Deduplication is not set up correctly. The browser pixel uses a random event_id while the server CAPI uses order_id — they don't match, risking double-counting. Needs alignment on a stable key (order_id). Reporting accuracy: purchase value must reflect the full order including upsells, with each conversion counted exactly once. gtm-tracking.php was copied from another site — item_brand/affiliation are hardcoded to the wrong brand and need correcting. STACK: WooCommerce, FunnelKit (Funnel Builder Pro, One Click Upsells), Elementor, LiteSpeed, GTM web + Stape server container, Meta Pixel + Conversions API, GA4. DELIVERABLES: Upsell events firing correctly through the existing GTM/Stape pipeline (the GTM side is already built and waiting on the dataLayer push) Working browser↔server deduplication, verified in Events Manager Accurate purchase value (base + upsell, no double-counting), confirmed via a live test purchase A short written or Loom summary of what was changed You must be able to validate your work in Meta Events Manager (Test Events + real traffic), not just configure and hope. Please describe a similar server-side CAPI + upsell tracking project you have completed, and briefly: how do you ensure browser and server Purchase events deduplicate correctly in a GTM + Stape setup?