Are these insufficient funds on long-standing accounts, or relatively new accounts? It seems like it would be pretty easy for a competitor to target a small gym by signing up several new accounts, paying for a month or two, then emptying all the bank accounts at once, causing transactions to fail. If the gym has 1.1K MRR and charges $100/mo per subscriber (that's what my private gym charges for open gym w/o personal training), you're talking about ~11 transactions per month. Failing 3 out of 11 transactions (27%) would probably trigger automated fraud systems.