What is the ruling on money earned from a percentage of the profits of a mixed (halal and haram) trading platform, as well as financial prizes received for users – who registered through you – reaching a certain trading volume in futures contracts, knowing that you previously stopped dealing with the platform?

If the platform offers both permissible and forbidden transactions, it is not permissible to generally direct people to it, except for those who are highly likely to restrict themselves to the permissible, due to the impermissibility of aiding in sin. As for the profits resulting from forbidden transactions, one must dispose of them, except for what was taken before knowing of the prohibition. Regarding the financial prize, it is permissible to take from it an amount proportionate to the permissible transactions. If it is impossible to distinguish, then half of it should be taken and the other half given in charity.