How it works
This is what revenue is made of and what ROAS is counted on. If the site sends a zero, a fixed number or an amount with tax in it, every money metric slides after it — and the ads will be optimised towards the wrong goal.
Example
The shop sent a total value of 180,000 across 300 orders.
Had the site been sending a fixed unit instead of the order amount, the ads would have seen a value of 300 — and the strategy would have optimised for the number of orders instead of the money.