In GA4, first collect the required action accurately as an event, then mark business-critical actions as key events. Older documentation may use conversion event for what is now a key event, so check the product and documentation date.
Using the action for advertising measurement and bidding requires creating a Google Ads conversion action or importing an Analytics event. Marking a key event alone does not automatically make it a bidding goal in every campaign.
Check primary or secondary action settings and campaign goals. Clicking an inquiry button, successfully submitting a form, and receiving a valid lead are different actions; document completion conditions and deduplication rules.