Primary vs secondary
Smart Bidding optimizes toward Primary conversion actions and only records Secondary ones for reporting, unless a Secondary action is added to a custom goal the campaign uses (see primary vs secondary conversion actions). Mark a shallow event like a page view or newsletter signup as Primary and bidding will chase it, flooding the account with cheap, low-intent conversions.
Choosing the right one
The Primary action should be the event closest to revenue that still has enough volume to learn from, a qualified lead or a purchase, not a form fill. This is the lever behind optimizing to the right event, and it pairs with offline conversion import and conversion values to point bidding at customers, not noise.
Common questions
What is a primary vs secondary conversion action?
Primary conversion actions are used by Smart Bidding to optimize; secondary actions are recorded for reporting only. Only mark as Primary the events you actually want bidding to chase.
Why does the wrong conversion action hurt performance?
Because bidding optimizes toward whatever is Primary. If a shallow event is Primary, the algorithm finds more of that low-intent action, raising volume while lowering quality.