I noticed something strange when looking at my iOS revenue graph today. Right now I average about $25-50 in revenue per day for my iOS apps. But on august 1 my revenue was actualy in the negative for that day! About -$200. How is this even possible and have anyone experienced it? What could have caused it? Can it be a "bug"? I am very confused right now, but I just want to ask a bit before contacting support about it.
If unsure, contact support, that's what they're there for.
Negative revenue can be caused by bounced payment (i.e. people using expired or stolen credit cards) or from people stepping down from their purchase (less likely). The bounced payments would explain, why it's only on one day, because those things are probably processed only once a month.
While these are possible explanation, I have no idea how Apple handles these things, so, again, I suggest you contact support. It could always be that there was indeed an error and you get your $200,-- back. ;)
$99/year for the developer membership, but $99 isn't $200 (unless you have multiple accounts) and that cost isn't factored in the graphs in question anyway, as far as I know. A chargeback or similar as mentioned by Rattenhirn is the likely explanation I'd think.