You've got to be wary of those self service machines. I'll explain what has happened to me at 3 separate airfields. The first occasion it was recommended that visitors entered the £250 limit on the pump, this I did and continued to dispense fuel.
Can't remember the amount I took, about £150 worth of fuel. Some days later I checked my online account which is solely for my flying, and is funded every month. The actual fuel amount was debited, there also being a difference of £250 between the a/c balance and available balance, the result being I'd inadvertently and unknowingly overdrawn.
Exactly 1 week later the 250 was added back to my available balance but not before I'd incurred a charge for being overdrawn, which after some wrangling was refunded. This has happened since, but I always enter the lowest amount, usually £50 which invariably goes missing for 7 days!!
Has this happened to anyone else?