Placed order rate
Placed order rate is the share of a message's recipients who placed an order within the attribution window: attributed orders divided by recipients. It is a send's conversion rate in Klaviyo.
How it is computed, where to read it
It depends on the account's conversion metric, usually Placed Order sent by the store. An account with no order metric (SMS only, an app) has no placed order rate, and KlaviBoard then shows N/A rather than a zero.
A stable placed order rate with falling revenue signals a shrinking average order, not an email problem.