Conversion shows up on the date the conversion happened, not the date the click happened. That’s the confusing part most people miss.
If someone clicks your ad on Monday and converts on Thursday, Thursday gets credited with the conversion. But the ad group that got the click on Monday is what gets attributed.
So you can have days where spend is zero but conversions show up, because those are delayed conversions from previous days’ clicks still inside the attribution window.
The 7 day window means a click today can generate a conversion showing up in your report anytime in the next 7 days. Meta goes back and attributes it to the original ad group but timestamps it on conversion date.
This breaks if you compare daily performance to revenue because the revenue hits on a different day than the spend. You need to look at cohort analysis or use 7 day lookback when analyzing performance, not same-day matching.
Reporting by click date vs conversion date would fix this but Meta doesn’t offer that view.