I just purchased 3 items and it did not add any additional fees, not even the payment system fee. I did not use any of the available credits I had and put the whole amount on a card. Maybe using available credits is bugged?

Thanks Iviy, maybe so.

There was a period of time that XSolla was adding a 'tip' on to purchases automatically. That it is $10 exactly makes me think that that might be happening.

Unfortunately I never actually used the service while they were doing this. Perhaps you can poke about and see if there is a drop down for such an additional 'tip' or 'service' charge?

I know Caspian slapped them down big time when they did this last time.

I am not sure if it is applicable, but are you taking into consideration an exchange rate of currency?

NVM This has been resolved. The error was my own. Thank you.