House percentage issue?

I am using paypal adaptive. I have set paypal adaptive to take 15% and I have set the website house percentage to 0%

Example of what’s happening :
When someone clicks ‘buy now’ on an item that costs £30. It will direct buyer to Paypal which says
‘Pay £25.50’

The buyer will pay £25.50 to the seller, THEN another 15% from the sellers Paypal is sent to my Paypal account (website owner)
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Paypal deducting the 15% and sending it to my Paypal is fine because I have set Paypal to do this and I am receiving this 15% fine. However the 15% which is automatically deducted when the buyer clicks ‘buy now’ this shouldn’t happen as the house percentage is set to 0% and and this 15% doesn’t go anywehere (not to me or the seller) it just disappears when buyer clicks ‘buy now’

I’ve tried to explain it the best way I can

Please help

Thanks