When you launch your ad campaign, our system will keep track of changes to your IG follower count as you run your ad.
It's technically impossible to tell you if a person followed as a result of interacting with your ad, we simply track the netchange to your follower count.
In an ideal world, we'd be able to place a pixel to tell us if someone followed but it's impossible to do.
You'll want to keep in mind
We're tracking the net. That means other organic followers will show up in the campaign reporting as you can't distinguish whether the follower came from the ad or not
Unfollows on IG will bias your reporting. As we track the net, let's say you got 10 new followers with your ad and you had 10 people unfollow. This would show that we've technically had 0 growth in the reporting, but we actually did grow 10 followers. If you dive into your IG's business insights you can actually get a breakdown of new follows vs. unfollows.
This is basically the best tracking for this type of ad technically available, but it's very important to try to account for any organic growth that creeps its way into the reporting.