What is the ruling on my earnings from someone subscribing through me to a website for gaining visits, where I earn 20% of every purchase he makes, knowing that the profit comes only from him and is not a network or pyramid profit? And if it is unlawful, what should I do with the money I possess?

It is permissible to promote websites and products if they are lawful and permissible, and if purchasing a product or paying a fee was not a condition for engaging in marketing. The commission due for each purchase made by someone you brought in corrupts the contract due to gharar (excessive uncertainty) and Jahala (ignorance), unless it is a gift from the company. If these conditions are not met, then it is not permissible to participate, and any illicit gains acquired must be disposed of by spending them on Muslim public welfare or giving them to the poor and needy. If someone acquired unlawful money out of ignorance, then what has passed is theirs. However, if they acquired it knowingly, they must give it in charity.