The gross revenue shown on your dashboard is the sum of amount paid by buyers, without any fees subtracted. On the payouts tab you can see your account’s balance after any transaction fees are applied.
As an example, if you sell 2 games for 1 dollar each, your gross revenue is 2 dollars, but, payment processors will subtract out approximately 30 cents + 2%, so you are only netting 68 cents per transaction, so only $1.36 is available. (Note these numbers aren’t exact, as there may also be an itchio revenue share, and sometimes processor fees can vary based on the specific transaction, and account adjustments may affect your final balance.)
I suggest you read here: https://itch.io/docs/creators/payments#payment-processor-fees
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Hope that helps