Lets say it takes 2 engineers 3 months to build an another payment processor + failover, at $120k salary + 40k in benefits and taxes a year a piece.
stipes SLA was 99.980% uptime for the last 90 days
0.02% * revLoss > 160k * 2 * .25/year
OP's app would have to be earning 400mm a year. Not likely but possible.