What to open
Your contract and your latest fee invoice. Three values are enough to fill in the left-hand column: the subscription amount, the percentage taken from your takings, and the answer to one question — does that percentage include bank fees, or are they billed to you separately?
If you cannot find the answer to the third, that is already a result: ask your software provider, and compare what is recharged to you with your payment provider’s public rates. Any difference is no longer a recharge.
Open a third document too: your payout statement. A cost can appear on no invoice at all — because it is withheld by the payment provider before the money reaches your account. It then adds up to nothing: it is simply missing. Take one month, compare the total collected from your players with the amount actually transferred, then subtract what your software provider invoiced you separately. Whatever is left, if anything, is the item nobody ever showed you.