Another android dev with (much) lower volume here. Curious how you know about errors driving that 20% number. Is there a report somewhere with this detail or is it just inferred from customer emails? The only failures I ever see come through are declined credit cards or the regular cancellations from users who used the 15min refund window.
I bet at least 50% of failures are customers trying to use someone else's card, or habitual charge-backers. What is the experience for each channel 90 days in when actual chargebacks start hitting?