A conversion credited to an ad that was seen but never clicked
In one line
A view-through conversion is one credited to an ad the person saw but never clicked.
Why it needs care
Impressions vastly outnumber clicks, so including view-throughs raises conversion counts and makes CPA look better. The problem is that much of that increase would have happened without the ad.
Campaigns that bought more impressions gain the most, so blending click and view-through conversions into one column distorts the ranking between campaigns.
How to handle them
Separate them. Read performance once on click conversions alone and once including view-throughs, and flag campaigns where the two differ sharply. Those are your first candidates for a holdout test.
Should view-through conversions count as performance?
Reading them separately is safer than deciding whether to include them. Blended with click conversions they break comparison between campaigns and automatically favour whichever campaign bought the most impressions.
Do lots of view-throughs mean the ads are working?
Not on their own. Buying more impressions produces more view-throughs, which also raises the chance those people would have converted anyway. A holdout is what settles it.
Why do view-through numbers differ by platform?
Because each platform sets its own view window. Meta's default is 7-day click plus 1-day view, so someone who buys three days after seeing an ad falls outside Meta's view-through count but lands inside a platform using a longer window. The same conversion is counted in one place and not the other, so line up the windows before comparing.