We pull your reporting metrics straight from Facebook: what you see in ToneDen is exactly what you would see in Facebook's ads manager.
Facebook uses a Last Touch attribution model for reporting your ad campaign performance and conversions.
Here's how Facebook explains it:
"Facebook uses a last-touch attribution model, which means we will attribute full credit for a conversion to the last ad the person clicked or interacted with. If the person did not click on an ad, full credit is attributed to the last Facebook ad viewed If they clicked the ad, it will get attributed to click-through attribution. If they didn't click, it's attributed to the most recent Facebook ad they saw."
It’s possible people are being delivered your ads for one of your ad campaigns and then making a purchase on a different product where you also have your pixel installed. The purchase value of that sale would then be attributed to your other ad campaign.
More information: https://www.facebook.com/business/help/458681590974355