Normally when you run Facebook ads conversions campaigns for purchases, Facebook will try to get you the most purchases for the lowest cost. These could all be low-dollar purchases.
If you optimize for Value, Facebook will optimize with the intention of getting you the highest ROAS. In order to do this, you'll need to turn it on when configuring your events for Aggregated Event Measurement. It will take up at least four of your eight slots for ranking events.
