Set Up Facebook Purchase FC ROAS Event on Shopify with First-Click Attribution

We run Facebook/Meta ads for our Shopify store and need a custom FC ROAS (First-Click Return on Ad Spend) purchase event implemented. The goal is to attribute conversions to the first ad click in the customer journey — captured and stored from the visitor's initial session — and pass that data to Meta when a purchase is completed. We need someone with hands-on experience in custom Meta pixel events, first-touch attribution tracking, and Meta Conversions API (CAPI). Scope of work 1. First-click capture logic Capture the first ad click (via fbclid / UTM parameters) on the visitor's initial session and store it in a first-party cookie or localStorage. This value must persist across sessions so it's available at the time of purchase, even if the customer returns later via organic or direct traffic. 2. Custom FC purchase event Fire a custom Meta pixel event (e.g., Purchase_FC) on the order confirmation page, passing value, currency, and order ID — triggered only when the stored first click is attributable to a Facebook ad. 3. Meta Conversions API (CAPI) Send the FC purchase event server-side via CAPI as well — using Shopify's native integration or a custom solution. Event deduplication between browser and server must be handled correctly using matching event IDs. 4. Implementation via GTM or Shopify theme Implementation can be done via Google Tag Manager or directly in Shopify theme / checkout scripts. Please mention your preferred approach and reasoning in your proposal. 5. Testing & handover Verify the setup using Meta Pixel Helper and Events Manager test events. Confirm correct value passing, deduplication score, and event match quality (EMQ). Share a brief handover document or Loom walkthrough of what was implemented. Requirements Proven Meta Pixel & CAPI setup experience Shopify platform experience (Liquid / checkout) First-click attribution implementation experience Google Tag Manager proficiency Cookie / localStorage UTM tracking Event deduplication between browser & server Able to share similar past work Turnaround within 3–5 days