Flippa Tax Help

I have a quick question about flippa and taxes. I am new to flippa but have recently just sold a website. After selling the site and getting the money I was sent a tax invoice in my email account. I paid 15% success fee. The email said "Flippa Tax Invoice", "Thanks this invoice has been paid". So do I have to pay taxes next year if I continue selling websites or does the Success Fee / Tax Invoice cover my taxes and I should not worry? Thanks a lot!