Nothing is being ‘acquired’ in an Engagement campaign, there's no sale or lead being optimized for, just interaction with the content itself. Trying to calculate a cost per acquisition here is measuring something the campaign was never built to produce.
Ask your agency this instead
If we eventually want this audience to buy or submit a lead, what's the plan to move them from engaging with this content to actually converting?
Want the metrics that actually matter for a Engagement campaign? Open the tool and pick one.
Adamigo provided the Engagement-objective CTR, CPC, and CPM figures used here, along with explicit engagement-rate tier language that informed how the bands were set.