The referee must trade $100 worth of cryptocurrency in order to receive (and for the referrer to receive) the free $10. This is a lifetime value, and there is no time limit. The $100 worth of crypto trades can be spread out over numerous trades, or can be completed all in one. For example, the referee could do 2 trades of $50, or they could trade $2,000 in their first trade. Both of these would be eligible for the $10 free bonus.