The credit card tests had unique network patterns we could block.

We lowered our online donation limit. Above a certain amount it really is more ideal for a check or some other type of transaction. Though we've had a few people offer to just pay the 3% transaction fee on top of the multiple thousand dollar donation. For those we do a bit more manual process.

For a cost, Stripe also lets you put some additional rules on what type of payments you'll allow & how much info the person has to verify for the payment to be accepted.