95% Conversion Attribution Restored With Server-Side Tracking

A leading French marketing agency was losing client trust. Browser cookie bans and iOS ATT were destroying attribution — ROAS reports were wrong, optimisation was blind, and accounts were quietly churning.

Rebuild the agency’s measurement stack so every conversion is attributed accurately and ad platforms get clean signals to optimise on (Smart Marketing §6.9 measurement & optimisation).

• Migrated from client-side pixels to a first-party server-side architecture using GTM Server Container + Stape.
• Routed conversions to Meta CAPI and Google Ads Enhanced Conversions directly from the client’s own subdomain — bypassing ITP and ad-blockers.
• Hashed PII (SHA-256) inside the server container to stay fully GDPR compliant before any data left the EU.
• Filtered bot and crawler traffic at the server layer so ad algorithms stopped wasting budget on non-humans.

Data accuracy jumped by 40% and conversion attribution reached 95%. A year-long attribution gap was finally closed, CBO started optimising on real signals, and the agency’s ROAS reports became trustworthy again — restoring client confidence.