It says it clearly in the terms you agreed when you signed up.
9 - You must pay taxes for the first withdrawals from our site. This payment is calculated based on your earnings. This initial payment will not be deducted from your gaming account. You can calculate your tax payment by reviewing the following amounts. For earnings up to € 2,499, you will be required to pay a tax of € 225. For earnings between € 2,499 and € 5000 you will need to pay € 320 tax. You must pay a tax of EUR 500 for earnings between EUR 5,000 and EUR 10,000. For earnings of € 10,000 and above, you must pay a tax of € 700. For earnings of € 30,000 and above, you must pay a tax of € 1400. For earnings of € 80,000 and above, you must pay a tax of € 3850 . And these payments will not be charged to your gaming account. You can pay taxes with the payment methods on our site.