CPT vs CPA in plain language
CPT (cost per tap) — what you pay when someone taps your ad. CPA (cost per acquisition) — what you pay per install (Apple’s “acquisition” is usually an install, not a paying subscriber).
The funnel gap
Taps → installs → trials → paid subscribers. CPT and install CPA live at the top. Subscription profit lives at the bottom. Optimizing CPT alone is meaningless without trial-to-paid.
True CPA for your business = spend ÷ paying subscribers (from RevenueCat), not Apple’s install count.
How they relate
Install CPA ≈ CPT ÷ tap-through rate (TTR). Subscriber CPA ≈ spend ÷ paid subs.
What to optimize
Set max CPT from your profit cap. Judge keywords on attributed subscribers, not Apple CPA alone.