NZD tracked as USD — a 4x ROAS target was really asking for 0.16x

The situation

A New Zealand home goods DTC brand was running Google Smart Shopping campaigns with a Target ROAS of 400% (4x). The campaign was consistently hitting the target. But when the owner compared Google's reported revenue to Shopify, the numbers were wildly off — Google was reporting 6x Shopify's actual revenue.

The problem

Google Ads conversion tracking was importing revenue from GA4. GA4 was receiving revenue in NZD (New Zealand dollars) with no currency specification — defaulting to USD. $1 NZD ≈ $0.60 USD. But since GA4 reported the raw NZD number as if it were USD, $250 NZD orders were being treated as $250 USD by Google. The real 4x ROAS target in NZD was equivalent to targeting 0.16x in actual purchasing power terms.

What we did

1. Compared GA4 revenue (NZD values read as USD) vs Shopify NZD revenue — 6x discrepancy confirmed
2. Added explicit currency: "NZD" parameter to all GA4 purchase events via GTM
3. Set Google Ads to use currency conversion — NZD displayed in reports, bidding adjusted for real value
4. Reset Target ROAS to 390% based on actual NZD transaction values — maintained same profitability target in local currency

Why it worked

Currency specification is easy to overlook when ecommerce stores default their data layer to the store's local currency without explicitly declaring it. Google and GA4 both require an explicit currency code — without it they default to the account currency (USD for most global accounts). This creates silent inflation for any non-USD store.